I'd imagine whatever's controlling the USB port is pretty low level given it's "only" used for a data connection. Of course I know nothing, so.

Did you want to actually mount the 770 to the 'bot or use it as a controller? 'cause if you just wanted to use it as a controller, it'd probably be a lot easier to build WiFi into the robot; at least I'm sure there are devices out there operating under the 802.11b/g standard that allow simple commands to be sent back and forth.

An easier off the shelf way:
http://aircables.net/

Just slap one of those RS232 to bluetooth adapters onto the robot and go to town. You'd probably need to port minicom or some other terminal app to the 770 but you should be able to do RS232 without cables pretty easily.

David