Here is another option:

Bolt the R10 clamp onto a T adapter (two bolts). Bolt the T adapter onto the upper arm (maybe two bolts). Slide it all the way forward and attach your lens ring adapter. Simple, cheap, uses existing parts (ok, you will need some metric nuts for the two bolts used to attach the clamp to the T adapter).

With a very small modification to the T adapter, it could work. Instead of the slot, put two tapped holes.