Roger Moy always fills this gap with washers. He won the FT springer worlds about 11 years ago and generally hits lots of stuff with springers.
I would do this, or at least try it. I have now fitted a stock lug and shimmed the inlet hole in the stock so that there is no way on earth the action can do an unofficial SR and twang in the stock, there's nowhere to go. I've not shot the gun enough since to know how successful this new measure might be. The little dibbles I've had looked good though. As much as anything I'm now using a much shorter fixing screw which has to be good news.