Great idea, but I'd personally be more inclined to leave the stock button on and figure out a way to mount it to the brake lever....then you would have brake lights!
That's a GREAT thought. But the little push button has two problems. One, it's far from being anything even close to waterproof. And, Two, it's not quite tough enough by any means to keep up for the abuse that it would have to take.
Life moves pretty fast. If you don't stop and look around once in a while, you could miss it.. Ferris Bueller