I found the original adapter plate made by thurstmaster was quite flexible, allowing the throttle tilt  when using it, I've thickened it out and made space for 6x M5x12mm pan head bolts to give it a bit more rigidity.

All you need to assemble is two M6x20mm bolts for the throttle base, and then 6 M5x12mm pan head bolts to mount the adapter plate to the clamp itself.