[Thunderguts]

Couple of things:

1) Did you try a 12pt 21mm socket? A 12pt usually works better. You also really need to hammer the hell out of it to get it to fit. If not, try a standard size. It may grip tightly enough. If they are on so tightly that you stripped two keys, maybe not. Maybe do a few panic stops to get the hubs really hot before trying to get them off with a socket. In theory the hub will expand from the heat faster than the lugs.

2) Fill the lug with JB Cold Weld and force the key into it. Let it harden. I'd say there's a 50/50 chance that gets it off. It's not that the JB Weld will cause them to "stick" together so much as it will fill in the gaps between the worn splines and not allow them any room to strip past each other.

3) My last resort would be to cut a channel clear across the lug and then use one hell of a flat edge (crowbar?) to twist it off.

4) If all else fails, take it to a bad side of town. Jack up the car yourself so they don't drop it on the brake rotors and leave it overnight. Thieves are very resourceful.