If it's as stripped as you say, you'll need to drill a hole and then use a bolt extractor. The good news is that it is a large diameter bolt so you can use a large extractor - necessary because you'd break a small one. You will need a replacement bolt anyway, so order it and you'll be able to tell how large a drill/extractor to use. use a slow drill speed, a cobalt bit and (important) some lube on the cutting surface of the drill. You may also loosen the bond of the loctite by heating the bolt, not sure if there are any heat sensitive components touching the shaft - maybe some tech reading this will let us know.
I just replaced the combi switch and I could not believe the amount of torque I had to use to break that bolt loose! It is glued in with blue loctite so the spec is 200 foot-pounds for that size bolt (estimating a 1/2") but it felt like 500! (I have high torque experience from working on Alfas where 150 seems to be the average torque spec). I had to use a 3' pipe on a 1/2" ratchet and stand outside the car facing the rear. I was sore the next day.
If there is any hex left a "Sock-It-Out" tool may work but I doubt it. tool link