yeah thats the only thing I could think of Quincy... I do the same as you... mix it well, coat the tip of the brush (about 25%) then brush it out on scrap paper it and brush...
On my 1/48 SBD I am doing now I decided to use light gray to drybrush some spots on the body to simulate fading, and surprise!!! it ended up looking like a good silver! as in wear had abraded the coat... it kinda surprised me! I'll have to go back and drybrush some blue/gray over it to tone it down but I may be on to something! I dont imagine it would work as well over a olive drab coat but who knows? might even show up more!
the only thing I use silver, aluminum or steel for is drybrushing the floors of the cockpit where the rudder pedals go and interior areas... simulates shoes/boots rubbing along the tracks in flight... I saw it in a reference photo for an SBD when I was researching this build and I am sold on it! after looking at the WWII color pics I was amazed at how much wear was done in this one area.
For a silver NMF plane I would think white would work possibly? (try it on sprue or such first) I would stay away from the acrylics for drybrushing too... just personal experience.
A substitute might be a silver artists pencil, shave some silver off then load it into your brush and brush it on... ever since I started using it for instrument panels and chips in the paint I am a believer! I imagine it would work well for what you are doing too, and you could add pastel chalk to color it for good effect.