It should be technically feasible to use the SansaFuze as an FM receiver for the computer. i.e.: have the player plugged in and having it be charged while the computer has access to FM frequencies through the USB device. I guess it would just need some driver and some software to play FM. a VLC plugin maybe?
Assuming you were sufficiently motivated, you could probably write some kind of custom USB interface for doing that. I think it would be a very large amount of work however.
I’d settle for beeing able to play music while charging like i could with my old creative mp3 player
Sounds like a hard concept to do i think, but maybe try and contact the rockbox guys and tell them your idea