"uses a special welding electrode to dissolve the bolt out of the hole"

Electrical Discharge Machining (EDM)

Give it one more try using Pat's suggestion. Heat the end of the stud with a torch and push a candle up against it. As it cools, it'll suck some of the wax in between the threads. Then lay a hex nut on the end of the stud and weld through the nut hole to the stud end, filling up the hole with weld. Then you can try using a socket on the nut to twist the stud out.