Since every mouse is different, this hack is mainly about the idea. If you can operate a tiny screwdriver, you should be able to do this whichever way your mouse is put together.
1 computer mouse
1 #00 Phillips head screwdriver (small)
1 X-Acto or utility knife
I am going to do this with both a Logitech USB Mouse and an HP Wireless Elite Desktop Mouse.
Step 1: Find how to open it
Under pads: using an exacto top, carefully pry these up and keep in a safe place to reattach later.
Behind stickers: rub your philips head screwdriver over the sticker looking for indentations. These indentations may be a sign of a hidden screw.
The logitech was simple: one screw and the whole thing came apart. The HP will take some tricky moves...