There is nothing like over complicating a repair!!! Just do as I do though I must admit I have only come across this problem a couple of times, because slings on shotguns are not a very common or popular on this side of the pond. Any way back to the simple extremely cheap and reversible repair, Just put the correct size plastic screw wall plug in the hole and screw in the swivel there will be enough give in the plastic to time the screw. I have no intention of explaining how it is reversible.

The only lessons in my life I truly did learn from where the ones I paid for!