JBWeld is highly over rated by many folks. It is "just" epoxy glue and not some miracle goop. A good epoxy I'll grant you but still just epoxy. The filler they use in it makes it easy to machine once cured but it's nowhere near being metal like. In the end you'd be trying to "weld" the parts together by glueing them together with some plastic. And the first time you tighten the seat post into place that JBWelded tab would bust right back off.

Hillrider, I've seen epoxy get hot enough to soften and be able to push around into new shapes and return to the original plastic condition but it was a near thing where the glue wasn't heated to any sort of considerably higher temperature. So it was fine when taken to THAT extent. It may also depend on the type of epoxy. But I would not doubt that if it was taken higher it would alter the makeup and ruin it so that it would not return to its original state upon cooling. I'll have to try some outdoors where the fumes won't make me gag and retch...