Yeah that's right, we had a lot of laughs with that "nut" subject...
Regarding your concern, if the nut still have bolt inside I would use a small dremel took, drill a lot of tiny holes till you can break the remains, or at least machine a slot so you can use a flat screwdriver. If you need a new nut, how about welding two regular nuts together, shaving off the excess?
Raul