I don't know if they come in a size big enough, but those "easy outs" (may be called something else) from Craftsman do a pretty good job of removing rounded off nuts/bolts. If it's as tight as you say it may take some serious work to get it off. If you choose to beat on the next size smaller make sure you get a good heavy duty one as the last thing you need is a broken socket stuck on there too...
Use a chisel on one side on the nut and give it hard hit(be careful no to slip). this will give you a place to set the chisel for the second hit to turn the nut off. The nut will spin right off. When I bought my 300M chrome wheels the guy at the junk yard had the locks off faster then he could do it with the key.
This just makes buying my 7.5 hp floor standing air compressor a better investment every day. Just hook up the air gun, crank the pressure up and spin that damn lugnut off(hopefully not anything else).lol
They make a tool for that sort of thing. Unfortunately..odds are you won't be able to find one to purchase anywhere, but the shops do have them. Forcing it with random objects is a bad idea because you risk damaging the threads on the bolt, too. So yes a shop would be your best bet.
Yea, I had a similar problem on my front right wheel where one lug nut just would not come off. I had gone to the tireshop to buy some new tires and my mount/balance appointment was for 9am and so I figured I could wait for them for like 2 hours and I was sure they'd be done in like half an hour later. Well, two hours went by and I asked them if my car was ready and he told me no because they tried to take it off and their Snap-On socket broke because the lugnut is so tight on there. To make a long story short, I got my car back by their closing time, at 6pm.