How to deal with worn-out threads on binding post?

My speakers have Edison binding posts. The copper threads on the binding post have worn badly over the years, so that the nuts do not screw on tightly. I would prefer not to replace the binding posts, in part because the speakers weigh 250 pounds apiece (not easy moving/transporting them), and in part because the speakers are one-off and the designer is deceased. I use speaker cables with spades, and banana plugs are not an option.

Any suggestions as to how to get the nuts to hold the spades tight against the binding post?