The BT (and other wheel controls) seem to be a variable resistance circuit which is nominally open. Meaning, it's only a few wires which send different amperages (assuming volts are held at 12) to the HU depending on the button pushed. Or at least that's how I read the schematics:
It seems like a stretch to assume that the industry would have standardized how many amps trigger song forward, mute, etc; but maybe they have (which would make finding a compatible HU feasible).
For now, my rooted phone lets me keep it awake while in my car dock, so at least I don't have to unlock it while driving. That, and I programed the volume rocker to skip songs when long-pressed. It's just not on the wheel... X-(