Buy a set of bolt extractors from the hardware store... get the pricey ones. Soak everything in penetrating lube for a good long while (even a day in advance with regular re-lubings), and go at it with those. If you don't have any luck, get a torch and apply heat and give it another shot. If you don't have any luck with that, then just roast the bushing, saw the bolt out and learn the joy that is replacing suspension bushings.