I'm one of those who bought a coupla those beautifully-made 6mm thick clutch friction disc hub spacers from Esmir Celebic on the ADVRider forum. Great solution to an inherent design problem that BMW has consistently failed to address with a "Technical Revision". Like asking Sachs AG to supply a plate with a longer hub.
Incidentally, I hope you don't mind Dan, but I've slightly tarted up your excellent little 25 second clutch spline wear investigation video to make it clearer to other readers on forums like UKGser, R1150R.net, etc.
https://youtu.be/dw6xP7a4EfM
AL in s.e. Spain