Originally Posted by tabetha

The likelyhood of the bolt freeing from the captive nut and coming undone is doubtful but best chance would be to weld using shit loads of heat a old socket onto the rounded nut, or try to beg borrow steal a blowtorch apply as much heat as possible, it still may win and if so just drill the f&&&&R out and as said two bits of rod with nuts welded on slipped through hole works a treat, some go above the nut by cutting open the floor of car to reweld etc.
I weld a bit of cut coat hanger on to a nut, but use SS nut and bolt, with lots of coppaslip.
The reason irwin didn't work is the metal is too soft, I'd be amazed if any easy out worked, I have three different types of snap on ones and still wouldn't do it, if you want grind it off or if it snaps you could try centre punching then drilling progressively up to just under size then use a tap, might get away with recovering enough thread.
tabetha