Hmmm, all this talk of decals has reminded me of some military vehicle markings that I had some time ago (from Skytrex, a firm that some of you may also know from their O gauge railway involvement, though sadly they went bust a year or two back) - they were waterslide decals of a sort, but they didn't work in the conventional manner. As mentioned in the post above, they were printed "face-down" on their carrier paper, with a backing sheet that you peeled carefully away from the "back" side of the decal - the back was left slightly tacky, enough to carefully position the decal on the model still with the carrier paper attached to the front of the decal - you then wetted the carrier paper, this soaked through and released the decal, which was still stuck in place on the model. You would carefully peel the carrier away leaving the decal, which you then VERY GENTLY burnished to press it securely onto the model. A varnish spray was strongly advised to protect it once it was dry.
Sounds rather like the Methfix method described, although this was achieved with water only.
Jon.