There is a post here saying to jack the car at the rear by the differential cooler. The BMW recommended jacking point is the black differential casing in front of the cooling vanes. There is a small "ridge" which helps identify it. It can be a PITA to get to with a dropped car and after market exhaust. I use a hockey puck as a pad
I use this method:
http://m3.madrussian.net/diy_jacking.shtml