You have four options. Three involves ruining a socket. The other doesn't

First you can try taking a slightly smaller size 12 point socket, hamming the hell out of it onto the lug and try to turn it off slowly.

Second, same concept but freeze it with freon and then put the socket on and let it get hot.

Three, tack weld on a socket that fits over the lug and loosen.

Four, just get a damn reverse thread big socket from Sears or something. It has grooves inside of it to grab on to anything and twist.