Smash through the two or three pegs glue together in the back of the stock. Yeah, it may sound violent but it won't break your gun and people have done it before. Works fine.
Pry open the back as far as you can and find an angle which you can hit a screwdriver into there.
Or you could just cut them with a dremel of a hacksaw, but it would be harder.
Ok i think this might work but i'm gonna have to try it later but now i'm getting ready for my day