If you're not going to reuse the studs - or if they're already unslavageable - I've had good luck taking a grinding stone or a die grinder, grinding two flats on the stud (don't thin it out too much, but chew the threads down and make a "flat side" on opposite sides,) and grab the stud by the two flats with your vise-locks.
It also comes in handy to fetch it a light rap or two with a light hammer right on the end to break loose any sort of rust, dirt, or crud that might be holding it in place.
If it REALLY sticks, heat the end of the stud up to a medium to bright red with a torch, then touch a candle (or block of paraffin wax, should be available at a place that carries canning supplies) to the base. The wax will melt and wick into the threads, and the hole will be temporarily expanded slightly by the expansion of the stud due to heat. The stud will shrink a touch faster than the hole it's in - which is why the paraffin will wick into the threads.
Let it cool to ambient temperature, and you should be able to screw the stud right out (it's how we also get oil galley pipe plugs that have been stuck in place for 30 or 40 years...)
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