According to this page:
http://realoem.com/bmw/showparts.do?...44&hg=84&fg=10 it seems to be the same combox regardless if you have 644, 6FL or both. So I guess all it would take is some re-coding to enable the Bluetooth interface in the computer. (Like switching the Bluetooth switch on your laptop). Worst case they need to add some sort of Bluetooth antenna.
They would probably still charge you enough to buy another combox though....