Cutting the nut possible too, but may be shrouded by the hub until it's a bit further.
I'm assuming you need a helper to push the brake pedal as there's quite a robust and effective anti-hub-spinning device you've got the screwdriver wedged against

I always put a couple of wheel bolts back in the hub before doing or undoing the hub nut. The forces are then not resisted only by the (two) M6 disk retaining screws. I've mushed the end of the driveshaft slightly in the past too. Always hit a punch now (sat in the dip in centre of the shaft) as fearful of ending up in your situation.
Stick some pictures up of how far the nut gets, can better advise if know scale if the mountain to climb!