[Arran]

Mike;
Another method I thing may work to ground an electrolytic can would be to solder a lead to a large star or locking washer under the can, some makes used to do this from the factory, some will just pinch a wire underneath the can itself, and hope for the best. I had not thought of using a copper rivet through the can though, that was a good idea, if you can find the correct flux you can solder to aluminum, but how long it will last is a guess.
Regards
Arran