It's probably possible, I am using my Stock Navigation screen in my Lexus GS430 to run a Xbox. I originally used a composite to RGBs converter (spliced in between the nav screen and nav computer with a 4PDT relay), but it really sucked as far as brightness and clarity. So I found some information and used a component video to RGBs converter (Audio Authority 9A65) and the difference was astouding, just as clear and bright as the stock navigation graphics.
However, the "composite" video sync frequency that is required on the stock Lexus nav screen is around 15Hz (not sure on the BMW, but probably similiar), otherwise you get garbage on the screen. So you can't run anything with a high resolution on it, I originally tried running a X2VGA adapter and it wouldn't accept 480i, 720i, 1020i, but would accept 480p...but the sync signal was too high so all I got was a rolling, fuzzy picture.