depends on what you have in mind. Photorealism is possible, but you're going to severaly tax your PC or Mac..;)
Sounds like you could do 2 renders, then use another program to go between them (there's bunches on Nonags.com, Shareware.com, Ulead, Sourceforge, the list is endless.;)

I wish I'd said that.. The Staircase Wit

anahl nathrak uth vas betude doth yel dyenvey..;)