I'd simplify it. Rondo for Calderon and Davis. The Raptors get an upgrade at PG, and while they give up a nice prospect in Davis, they have the European kid coming over possibly next year, to put next to Bargnani, so Davis is replacable for them.
For the C's, they get a PG who fits in with their core a bit more, because he can take some of the scoring burden off the Big 3, while still being a good passer. Plus, they get a very talented young big man to try to groom.
I know its not the type of deal that blows you away, but this is probably the type of deal we would be looking at for Rondo. Quality replacement, plus solid prospect with high upside.