Unhhh, I’m lost. The throttle stop is on the primary throttle shaft, and unless you have a leg that pushes the throttle pedal through the floor, that should suffice. I’ve never run a secondary throttle stop on anything.
That said, as mentioned above, you can set it up so the cable just pulls the throttle to WFO and you have all the pull you can get. That way you won’t be able to leverage the cable enough to damage the throttle shaft.