This is probably the most dangerous way, but it worked (I have done it a couple of times). Anyway, I needed a LOT of that color. I inverted the can, depressed the nozzle to get all of the spray out of the pickup tube and kept going until propellant was gone.. Then, I set it down on a bench upside down and pressed the can down so that it allowed any additional propellant to vent while I worked.
I then used an awl (a solid metal one able to be hit with a hammer) to poke a hole in the bottom of the can. I quickly enlarged the hole with a reamer until it was about three eights of an inch. I then punched another hole near the top of the can, then poured contents into airbrush jars. A bit messy, but it worked.
Safety disclaimer- do NOT do it this way, but it worked for me :-)