The starting point is finding a remote control that transmits Bluetooth directly to the G1 (i.e., not infrared or wired). It needs, at a minimum, a forward and a stop button. Reverse, pause, and other functions are nice, but not mandatory.
The other half of the solution is software to control the media program in Android, which may or may not already exist; if not, I'll commission someone to write it. Maybe I can even offer a turnkey system for sale if there's enough interest.
I know someone's will say "search the forums", and I did. What I found seemed to be focus on wired remotes for another HTC phone, or remote controlling your PC with your phone. But if I missed a relevant post, please do correct me.
Ideas are greatly appreciated.