the iDrive control will eventually let you select the video source (there are 3, i believe) from your iDrive... are you sure you searched and read other threads? because it really doesn't seem like it... here's the thread --read it from beginning to end this time:
http://www.e90post.com/forums/showthread.php?t=15267
(i'll give you a hint, read the very last post in that thread)