IIRC, the iPod Classic and the iPod Nano 3G have more or less the same hardware inside, and I also believe (but I could be wrong about this!) the same firmware, if not extremely similar. What is needed is to figure out if the same exploit that allowed the iPod Classic to get a Rockbox port is also on the Nano 3G, and if it is, that should make getting a port onto it a snap.