It will definately leak just using two studs, as the system is pressurised, you could try slapping loads of sealant round it and hope for the best, but depends how much you have to use the mini.
Why not just whip the stud out and replace it?
Easiest way iv always found using random bits you will have lying around is drill a small hole in the middle if the broken stud, then hammer a star pattered "drill bit" not sure the exact name, and undo using this.
The main reason the snap is dues to corrosion between the aluminium housing. So once you start undoing from below they usually come straight out, if not just drill out and tap a new thread....