Well, an update on this problem. After 'cementing' with JB Weld, I have found another NOT-use for that product. So far, I have found nothing at all that it can be used for successfully. After curing overnight, once the repair heated up, it stank royally - and smoked profusely - as the exhaust heat proceeded to incinerate it to a crumbling carbonaceous mass. This continued to a lesser extent for a couple of days until the rattle was back as bad as ever. The best I can say is that at least the remains were easy to clean up in preparation for another repair attempt.
This time I got an exhaust system U-clamp (2"), crimped the heat shield down to the pipe, and clamped it. I think I may hear small 'pops' as it heats and cools, but I don't expect the rattle to return this time.