I don't see why packing a shimano cassette body, prawls and all, full of JB weld wouldn't hold. The prawls will be locked into position against the inner track surface of the body for forward movement, and for backpedaling the prawls will A) be "glued" into place, and B) be "wedged" into position from underneath .
I doubt the torque from a wheel could come close to compressing a solid wedge of steel and JB weld.

Try it out. You're running a brake so the worst thing that could happen is that you lose drive and have to walk it home.