Okay so I know you're looking for a custom mouse, but I have to recommend the one I'm using. It's extremely cheap for a gaming mouse, and it comfortably fits every finger on a medium-large size hand.
It has a double click function, Glowing LED's ooooh, and 3 other programmable buttons on top of your regular left-click, right-click, & scroll wheel.
Unfortunately it's Japanese, so some of the software for installation will probably be in Japanese.
Please check it out though, I wouldn't post if I didn't feel like it was worth a look.
It isn't ambidextrous, so that might be an issue.