I went to a paint and hobby store today and I actually found plastic films with a really realistic marble texture. I should probably be able to use these for a material finish, just like Brian Calvert did in this tutorial: http://projectguitar.com/tut/mat.htm
These films, or contactplastic as they called them, already has glue on one side so they seem to be relativly easy to attach. I just need to try it on a test piece first. They are semi transparent so I should paint the guitar in marble white first, and they will probably stick better to paint than to bare wood. Need to find a good lacquer that works with the plastic too...
Anyway, I feel a little more confident now!
What do you guys think? Good idea?