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This JB Weld trick sounds like a proper evil genius hack if it works.
A less genius approach would be to simply araldite (epoxy) a pedal into the crank, preferably a pedal that is easily serviceable. Clean the crank and pedal threads first. Obviously it's never coming out again but should still be serviceable.
Ndeipi-
JB Weld is basically epoxy with very fine bits of steel in it. When it sets it has similar properties to steel, but with a lower melting point.
It's very handy stuff. Just don't buy too much of it - it's a favourite with underworld armourers for making very illegal soft-nosed bullets.
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I wondered about epoxy, but since it's coming down to a feather edge, my feeling is that it would be too brittle. I wondered about isopon (or even the two-part wood filler that smells the same), since it's really tough but doesn't seem to set quite as crispy as epoxy.
Brommers
ffm
It's a bodgy old hack, but I've seen this work before:
JB Weld is amazing stuff. Part of the engine block on my old race car was held together using it, after I cracked it overtightening a tapered oil pressure sender fitting. If you don't add enough grease to the pedal threads, and the JB Weld bonds the pedal to the crank, it's never coming out again without copious amounts of drilling.
The other option is to build up the damaged thread with JB Weld or (if you have an AC TIG welder) with weld, and then retap it from the back, but that requires a 9/16" tap. And possibly an AC TIG welder.