Doesn't look real easy. I think the way that I would do it is drill another smaller hole on the edge of the existing hole. Use a hanger to fish the nut into the right place and thread a bolt onto it. Then weld the nut to the frame by filling in the hole I drilled.

Not the easiest solution, but that's how I would probably tackle it.

Maybe Lee can post some comments as I thought they put an extra one on yellowjacket.