Here is a thread with a previous discussion on the topic, and APW2607's home-made solution. Read the two links in my post #2 there:

http://www.xoutpost.com/bmw-sav-foru...bike-rack.html

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue