The idea is to avoid smashing the fish.
You can buy sheets of filter material, or sponge material or something similar at the LFS (usually). Once you get the fish out (if the decor is not broken) I would plug the holes with something like that. Also, do so if you replace the decor with a new one. You can find ways to create caves and hiding places for him that he cannot get stuck.
If you are sure he cannot get out, you could try to enlarge the hole. As long as the fish isn't right against the hole, you could stick a hammer head in there and apply leverage to break it open a bit wider.
I agree, hold it upgright so it is retaining water and try to nibble the hole larger.