Since neither Hound Knight or Atlas (Matt) has replied to my numerous FMs, I took the plunge and came up with a rudimentary template for the arms.
I've saved this in the same resolution as the 8 Aug 2009 WIP version - i.e. if you downloaded this, pasted it into a MS Word document without any resizing, it will come out actual size.
The arm template was painstakingly developed from playing around with paper, sticky tape and marker pens all over a minifig.
I have yet to try printing the actual arm templates out, but should anyone wish to beta-test the arm coverage, I suggest using those plain white mailing label sticker papers - if your printer supports it, that is.
As for whether it's possible to actually apply the decal onto the arms, I know that softening the decal sufficiently enough to conform to the unusual anatomy of the minifig arm is possible (See Kaminoan's example - since he is not in a position to give away his IP, I had to design my own template myself, y'see).
If all works out, I think I can make a decent start on those Class A decals.
Happy experimenting, folks!