It uses a microswitch like
the last three on this page. So far I've been re-bending the small copper tension spring that's inside this switch, but it's a pain getting the spring back into position.
Edit: Actually, this is the exact info off one of the switches from inside the mouse, found my text file I saved on it in case I had to go that route:
Omron
2968RN7
D2FC-F-7N(10M)