1. Just remove the FSB altogether until you can get this issue sorted.
2. How much space is between the top of the broken stud (blue) and the next section of subframe (red)? Is it enough to fit a decent sized nut in there?
3. How do you expect to replace that stud even after acquiring a welder? There is no way you're getting a new stud through the top of there. That red part of the subframe was welded to the rest of the subframe AFTER your broken stud was set into place at the factory. Not sure what your logic is behind this...