There'll be no master key solution Rog, and it's my understanding dealerships don't cut keys, they order them from Germany. It would be feasible for a locksmith to cut one from a blank if they had the appropriate blank (available on eBay - time ...) and the dealership provided the key code (which they will only do on proof of ownership ...).
If the new owner would trust you with the key code, or a clear photo of the key, these people may be able to help in your time frame. The key would not be a transponder version, so won't start the bike - just open the under-seat lock and top case and new panniers if he has them fitted
BMW Motorcycle K5001 - K8276 SERIES keys cut to code We supply every commonly used BMW motorcycle Key, used on a range of classic and modern motorcycles,
www.key2code.co.uk
You could re-key the locks to your own bike some time later and maybe send the then obsolete spare to the owner of your old bike.
Given the housing is plastic, drilling out could cause damage to it.