Yea I went through the same thing and detailed the answer in my review.

First I took a hitec servo arm that I had cut off the cyclic servo. The screws thread right into them, unfortunately they are too short to thread through the ball, the futaba servo arm and into the hitec servo arm that I was using as a sort of plastic nut.

So I ended up taking a flat grinding stone to the Futaba servo wheel and milling it from the bottom to reduce the thickness of the arm by half. You dont have to do the whole thing, just where you want to put the nut plate. Then the screw went down through the ball, through the reduced thickness futaba wheel and threaded into the hitec servo arm.