Inspired by the rainbow-plasma program, I patched the MeggyJr API to work on the Rainbowduino. It compiles and runs all the MeggyJr programs I have tried. Of course the Rainbowduino lacks sound and input hardware so the games are not playable but programs like plasma, binary clock, and text scrollers work nicely on it.
I have plonked it up on code.google.com/p/rainbowmcompat/ , give it a try. The instructions are in a readme.txt in the zip file.