Also, try Auto Advantage in Manassas. They are primarily a used BMW dealer, but they do pretty much complete service as well. I have not used them for service, but have bought two vehicles from them, including my X5. They sold me my aftermarket warrantee (from Ultimate Warrantee), so I sure hope they would accept it for service work. I can vouch for their attention to detail with prepping their vehicles for sale--it is at least as good as a dealer's CPO.
Here is their web site:
http://www.onlybmws.com/