It's very difficult for me to visualize, from the quality of the photos, exactly what you have. That being said, you can get a small piece of 1/16" aluminum and cut out a shape that can be screwed down to the existing arm. The ball link can be attached to this aluminum. You can use JB Weld between the aluminum and the original arm.

Many times I have had the same problem that you have and have had to think it through.

You might want to contact BCMA and ask them how they suggest connecting to the throttle.