I've just stumbled across an update to the SteerMouse driver that was originally only for Apple's Mighty Mouse (I think).
Their newest version supports additional USB + bluetooth mice, I had hit and miss luck with controllermate and gamepad companion (neither would get the browse...
I'm hoping to find an answer to this as well. I've been able to make the mouse fully functional using the GamePad Companion (carvware.com). But it would be nice to get the multimedia buttons functioning. USB Overdrive has a note on their site that the next release will have bluetooth support...