Man, that's awesome. I wanted to find some of that super dense foam they use for flower arrangements, and build a mold that could be used for plaster-of-paris models... I haven't had the time or energy to make it happen though. I don't know what kind of quality they'd end up being either...
Care to share how you do it? I've read a lot of stuff for making the kit models more realistic, mostly from this site:
http://www.briansmodelcars.com/
The guy can do crazy things.