I struggled with this too and found a procedure that worked well for my 4.4 2005. After following the procedure mentioned here, I additionally did this other procedure (using a cooling system pressure tester as mentioned in Bentley manual) and much more air came out of the cooling system. Eventually the coolant spewing from the bleeder screw had no more air bubbles.

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