man unfortunately, that's a good question for the stealership. Not many around these parts are privied to such crafts. You might also try posting in the 5er section of this site. You were correct in coming here, but I doubt any who come here would know.
It will be one of two scenarios:
1. The car was prewired for satellite and has all the necessary periphials already installed, requiring merely a call to Sirius for activation. (most likely scenario)
2. You would have to have the stealership install your satellite receiver that would interface with a prerun DIN cable in the boot. Then you would see that option on your iDrive.
Either way, there should be something mentioned about accessing the system in your manual. Better yet, if the Satellite tuner is preinstalled, there should be a VIN# and a Satellite ID# in your manual packet. These are necessary for activation.