Im still a little confused on the button. Could you do an exploded/side by side pic of that. Each part next to each other in order from left to right, as they go together?
Sheep - The button is just a plunger to push the battery up to make contact at the other end of it. You could use anything to make it as long as it fit inside the spring. Even wood or plastic.
You could drop a bolt in the hole with the threaded end sticking out and eliminate the threading and tapping (and a bunch of work) and it would work fine. Again as long as the head of the bolt fit inside the spring.
Hope that helps. If not let me know and I'll take another pic or two.