Ohhh, just did something similar, this saved my bacon. I got it at Autozone, but probably many places carry the same thing or even brand. I got sockets that are brand name IRWIN and are called "Bolt Grip". You basically tap the socket on your rounded bolt, put on your drive/extension and it grips like crazy and out came my completely rounded bolt. I had to pry it out of the socket once it was out. Best $7 I ever spent.