This may be pretty extreme, but I had to do it to on a lawn mower recently. Got a free 6.5 hp B&S, self-propelled w/bag, but the PO had put on an aftermarket blade, and it started slipping once it hit the grass. First he used his impact wrench to "get it good & tight". When that didn't work, he tried to use it again to get the bolt out. Using his impact wrench on the 1/8" thick bolt head just chewed it all to hell. Damn thing ran GOOD, so I was determined not to let it go. First I soaked the bolt, of course. Next, I took a dremel and cut two opposite sides flat (making the head a rectangle. Then clamped on a large vise grip tight as I could squeeze it, then slide a breaker bar over that. One shove, and she came spinning right out. Maybe that would work? If i hadn't loaned my pipe wrench out and the bolt head hadn't been so shallow, I probably would have used that instead of vise grips. I think I could have omitted the breaker bar if I had.
Edit: Just saw you fixed it, sooooooo this would be for future reference. LOL!