OK, maybe not that secret. But I don't know anyone else who does it this way. After mounting the veneer with contact cement, I go over it with a hot iron, which briefly re-activates the contact cement, and then forces the solvents out, leaving just the bonding solids.
As a finish, I use automotive clearcoat, slightly colored with translucent tint to look as close as possible to a light varnish. I do not use any sanding fillers in the veneer, as I feel it detracts from the beauty of the wood, and often shows up more when finished. I use the clearcoat itself, applying it and then sanding until all of the grain and joints are filled. Once I can sand the piece and have nothing but dull, matte finish, with no low, glossy spots, I can build up several coats of clear for gloss and UV protection. I then wet-sand and buff the clearcoat to the desired finish, just short of a mirrored gloss.