For years, I've had the following setup in my car: a Kensington LiquidAUX and a Motorola Bluetooth hands free device that clips to the sun visor. The LiquidAUX charged my iPhone, took line-level audio from its dock connector, and controlled playback through an RF steering wheel remote. I'm considering replacing that LiquidAUX with a Bluetooth solution that would perform all the same functions.
The product I found that comes closest is the TuneLink by New Potato, but it lacks a steering wheel remote. I'm wondering if it's possible to get a separate remote that controls playback over A2DP without receiving the audio stream. If so, I'll continue trying to find a remote that will clip to the steering wheel, but so far, I'm surprised that I haven't found something like that.