Sure. It's pretty simple.
I ought to start, I guess, by emphasizing that I've only used this trick on fairly small-scale models (e.g., my little frigate Hancock, on 1/128 scale). I think it would look acceptable on 1/96 in the eyes of most folks, though.
The first step, as always, is to get a clear idea in your head about what the original looked like. The footrope, strictly speaking, is the horizontal line that the guys working on the yard stand on. It's suspended by short, vertical lines called "stirrups." Prior to about 1790 (or maybe a little later; Mr. Lees says 1811), the outer end of the footrope was fastened around the yardarm (i.e., the extreme end of the yard) outboard of the yardarm cleats by means of an eyesplice. The other, inner end of the footrope could be dealt with in any of several ways; the most common, during most periods, was for it to be eye-spliced around the yard a few feet on the other side of the mast. The upper ends of the stirrups were eye-spliced around the yard, and their lower ends were eye-spliced around the footrope. Sometimes the lower end of each stirrup had a thimble spliced into it; the footrope ran through the thimble. I've seen drawings that show the footropes with small "mice" raised in them - tapered, conical pieces of ropework on either side of each stirrup, to keep the footrope from sliding through the eye on the stirrup. The whole system was set up so the footrope hung about three feet below the yard.
With the introduction of the jackstay, in the very late eighteenth or early nineteenth century, the system changed. Now both ends of the footrope, and the upper ends of the stirrups, were eyespliced around the jackstay. From the modeler's standpoint that's a matter of some importance. Prior to the introduction of the jackstay, the footrope hung directly beneath the yard. If the yard had a jackstay, the footrope hung behind the yard.
Sometimes there was one other piece of gear. If the sail mounted on the yard had reef points, and was significantly wider at its foot than at its head, reefing it properly would require that somebody work out at the very end of the yard. (In eighteenth- and nineteenth-century warships, the only sails that met that definition were usually the topsails.) In such a case there was another, shorter, footrope-like line called a "flemish horse" (I have no idea what Flanders had to do with it). Its outer end was eyespliced to an eyebolt driven into the end of the yard, and its inner end was eyespliced to either the yard or, if the yard had one, the jackstay.
I think there's pretty universal agreement that eyesplicing thread, on scales smaller than 1/48 or thereabouts, is not a sane thing to do in one's limited time on the Orb. (Even if one's eyesight and dexterity were up to the task, I'm not sure it could be done effectively to scale.) So for modeling purposes all this gear can quite legitimately be simplified.
My favorite material for this particular job is brass wire, but copper probably will work just as well. A model railroad supply company called Detail Associates sells brass wire in packages of nice, straight lengths in lots of small sizes. I always pass a piece of it over a candle flame before doing anything else with it; the heat softens it and takes all the spring out.
I like to do as much of this kind of work as possible before installing the yard on the model. (I generally clamp a piece of dowel, about the same diameter as the relevant mast, in a vise on the workbench, and secure the yard to that while I'm working on it, then transfer it to the model when it's ready to go.) The other necessities are a small soldering iron, some solder (preferably lead-free), a package of straight pins, and some sort of "soldering pad" - a fireproof surface that things can be pinned to. (Micro-Mark sells soldering pads made for the purpose; a scrap of wood will work if you're careful.)
Figure out the spacing between the stirrups (which should be marked on the rigging plan). Cut a piece of wire somewhat longer than each stirrup, and form a small eye in the end of it with needle-nosed pliers or tweezers. (Here's where having annealed the wire in advance will make the job easier.) You've just made the first stirrup. Fasten it down to the pad with a few pins. Make the other stirrups and pin them down the proper distances away from each other. Cut a piece of wire to form the footrope itself; make it quite a bit longer than it needs to be. (Wire is cheap; better longer than too short.) Thread the footrope through the eyes on the stirrups, and put a tiny drop of solder on each joint. Now you've got the basic footrope-and-stirrup assembly.
What happens next depends on whether the yard has a jackstay or not. If it doesn't, form the outer end of the footrope into a loop that slips neatly over the end of the yard, solder it, and trim off the excess. (For this kind of wire work a pair of really small wire-cutting pliers is a nice thing to have - but an old-fashioned nail clipper will work fine. Cutting softened brass wire with it will wear out the blades eventually, but the tool is cheap and easily replaced by any drugstore.) Install the footrope and stirrups on the yard. If the yard is wood, you can form the necessary loops in the other end of the footrope and the upper ends of the stirrups, and solder them. If the yard is plastic, please don't get a soldering iron near it; form the eyes, snip off the excess, and put a drop of superglue on each.
If the yard has a jackstay, use the same system but secure the upper ends of the stirrups and the inner end of the footrope to the jackstay. If the yard is supposed to have a jackstay but you aren't reproducing it (jackstays are mighty small; lots of good modelers omit them on scales smaller than about 1/64), a good way to fake it is to drill a hole in the top of the yard where the ends of the stirrups and footrope would be located. Make a tight bend at the appropriate spot in the wire, snip off the excess, and superglue the wires into the holes.
Throughout the process, measure carefully. The footropes need to hang three feet below the yards - and if one of them hangs lower than that, it will stick out like a sore thumb. Also, allow for a little "sag" between the stirrups.
All that, as usual, takes about 1/10 as long to do as it does to describe. Fitting the footropes to a yard shouldn't take more than ten or fifteen minutes.
Hope that helps. Good luck.