Front rotor allen bolt stripped, now what?

[N2MYE30]

5.5mm allen with a hammer. I cannot remember the standard size thats a bit bigger than the 5mm but same concept. Hammer the larger allen in as far as you can. BTW, this has happened to me several times...what a pita! I now stock new rotor screws.

[foofopps]

So I'm doing my brakes all around, pads and rotors. Im done with the rears and had no issues. On to the front and the driver side 5mm allen is stripped out completely! Has anyone had this happen to them? What should I do? The only thing I can think of is 'carefully' taking the rest of the allen head off with a grinder, then pull the rotor off and I'll have a bolt that I can work with. I used PB blaster prior to it stripping out. Any better options before I go to town on this with a grinder?