When I took up shotgunning, I had a lot of trouble with the stock coming loose. I, too, found using a screw-driver awkward.
But, it's a slotted hex bolt head and I found that using a nut-driver *much* easier. In the event, I made a special "M37 Stock-Driver".
Take a length of, say, 8mm bar. Grind a 1/4" square on each end. On one end, fix a 3/8" (or whatever it was) socket. On the other, a Philips / Pozidriv / whatever screw-driver bit for the two butt-plate screws. Finally, weld a short length of bar at right-angles near the screw-driver bit. Et, voila! A tool that makes things *much* easier.
What's really annoying is that my stock cracked and so I acquired a Choate plastic stock; the hex head is a different size thus making my tool useless...