I'm with Bruce for a quick fix,
If for example it's a 10mm thread, run an fettle it up with a file and run 8mm die / die nut down it far enough to get a full nut on then pack the rest out with washers.
If you want to get it out, weld a nut to the stud the whilst it's still warm, hammer it like a nail, without bending it, and as it cools 'rock' it both ways whilst applying you favourite penetrating fluid..
Should it snap, drill the stud out oversize, tap the hole and make a hermaphrodite stud - 12mm one end and 8mm the other, if you haven't got the new hole quite central make the stud offset and fit it with a good dollop of Loctite
Finally as my avatar says, run the nut down as far as you can and then weld it to the stud and leave 'til next time.........
I know the answers are 'cringe worthy' in the eyes of a lot of guys but if you're working with limited time / kit / money ect. then bush engineering is better, by far, than waiting for Fedex
Cheers
Stef