NabazLab (http://nabazlab.sourceforge.net/) seems like it may have been doing the closest to this, if I understand it, but it's hard to follow the English documentation.  It also doesn't seem to have been updated in a long time. 

There seems to be far more activity on the french forum than on Nabaztalk.  I don't speak French, so I don't know what's there.  It's at
http://nabaztag.forumactif.fr/  Maybe there's something there.

I just received a Nabaztag/tag rabbit and was wondering if anyone has tried digging into its firmware. Basically, I'd be interested if there is a chance of modifying its system or at least adding new capabilites to it, so it will not permanently exchange packets with that french server.

I'm not talking about setting up proxies locally, but would rather see my application code being executed directly by the rabbit.

Cheers,
Herman