Just found your post, so you probably are not even going to get this.....
Dude, this to me seems like a no brainer. Go to the junk yard (any of them within 200 or 300 miles its worth it, and pull the wiring harness out of the same car. To be sure, you will need to check the VIN to make sure that the build date to the junk car and your car are similar enough for you to do this. It will still cost a bit, but be cheaper than the stealer. Pull the pass. seat out and start matching up stuff ONE BY ONE. Do NOT pull everything out and go at it. Now, this may not work because you might get 'open loop' issues. But, at least you will get the part cheaper. I don't know what the stealer would charge to install, but at least you got the part and took a shot. They also may not do the work because you are not using a brand new one. Maybe you can hit an independant shop that speacializes in BMWs????? Good luck