http://www.amazon.com/VicTsing-Wirel.../dp/B00NMD4ZCQ
A very late addition to this thread but if anyone's interested I just bought a couple of these (one for my E90 and one for the wife's Corsa) and am truly impressed with the way it all just works so well out of the box. The quality of the audio is also high (full stereo). An amazing product from the Chinese for once!
The unit plugs into the cigarette lighter charger slot and the attached 3.5mm audio cable plugs into the AUX-in port, bothk under the arm rest. It also comes with a USB slot, so you're not giving up that charger slot! Simply pair your phone's "Media audio" to the unit and keep the "Call audio" paired with your car's own Bluetooth. Both connections stay alive! Then select Aux as the audio source via your CIC. Works perfectly with an Android phone (not sure if iPhones can maintain two separate Bluetooth connections)
Cheap, simple and reliable. You can't go wrong and every BMW owner that is unable to pair media audio to the car's own Bluetooth should get one!