If your capable of doing the service yourself, sign the book yourself and keep all the receipts for parts and stuff. Euro rules say we don't have to take it to a BMW dealer for servicing now anyway. The only problem is BMW are the only company with a GT1 diagnostic machine, but there are plenty of others that can do the diagnostics but not reprogram. I have a 911 diagnostic it's cheap £100 but reads and clears faults which is all I want it for, there are more expensive one's out there.
99% of services you can easily do for yourself, the 1% get a dealer to do.
Or talk to the dealer and ask if you do most of the service like oil change and valves will they do the technical stuff to keep costs down.