I generally fit buttpads by wrapping one thin layer of masking tape on my stock, installing the pad, then using a disc sander to mate the contours together. Easy peasy.
I’ve done it also with a bench mounted belt sander, a handheld belt sander fit into a bench vise, a drum sander with a collar jig and guide cap (kinda worked like a guided flute bit on a router, but with a sanding drum), and with hand tools. Disc sander just works easier for me.
But…
There’s not a chance in hell I would unduly modify stock fit just to chase eye relief on a scope. The stock should fit our body, and the mounts should position the scope in front of our eye. Mounting solutions exist, and even making or having made custom solutions really isn’t so difficult. Shortening a properly fit stock to chase a scope is cutting off your nose to spite your face.