Shredlife has the best solution. Heat is the standard method for red loctite removal. This is super easy with metal parts, but you need to work carefully. Do as Shred said and heat the shaft of your screwdriver and keep as much metal to metal contact as possible. Use a small hand held propane torch and keep trying to break it free as you apply heat and be carefully not to overheat and take too much time.
I would also keep a can of water handy to cool the insert as soon as you get the screw out. Also, allow the board to completely cool before going on to the next screw.
Applying heat will damage both the binding and the snowboard around the inserts. Don't use heat. That's great for bolts on a car - but even on a car you don't use a torch if the bolt you are loosening is near rubber lines or wires or anything else that will be damaged by heat. By the time the nut expands with heat to loosen a touch, those wires or lines will be trashed.
The impact gun will take care of it, no heat required.
There were some good suggestions here for cutting a slot if required to use a flathead if the screwheads are too far gone. You might cut a bit into the binding disc, but probably will be OK in that respect as well.
Good luck - minimize collateral damage - don't use a torch.