The double nut idea to get the stud out is a good idea. If the nut doesn't hold because it's still too tight and you don't care about saving the stud at this point, weld the nut on.
Once it cools use an impact wrench to unscrew the stud. Impacts seem to work better than just a ratchet, especially if you kind of feather the trigger a little to keep from twisting it off at the weld.
