Gas welding maybe, but arc welding NOT, because If you were going to clip the ground to anything but the bolt itself you would probably weld the bolt to the block. You're probably way ahead of me on that, but just incase.
I don't think it would hurt to heat up the broken bolt and try to kill off some of that rust, either that or soak it with some Liquid wrench. If you have 1/2 inch left, try a good vice grip or pipe wrench to turn it (Insted of welding a nut on it). With all that said, I haven't had to do this on my VX, just other pojects around the farm, so take it for what it's worth.