arran transfer uv's is the way to go , the uv's have nothing to do with the texture you apply only the way the texture fits the mesh,so simply create the textures you need be it 2, 3 or 26 whatever using the one UV map.

Then create a shader for each texture and then after all the keys have their Uv's transfer mapped just apply the appropriate shader to the keys you need it on.

hope this helps.