It does sound like it just gets him too over excited - my old cat Ash was like this - not peeing, but he would be really unpredictable and sometimes accidentaly aggressive.
He would also scream and yell, get him self all wound up, frustrated and ultimately quite upset. He couldn't even control himself long enough to play and enjoy himself.
Our vet said that, in a few cases, some cats are just hyper-sensitive to catnip (like some people can't handle caffiene), and recommended valerian-filled toys. It acts like catnip, but seems to provoke fewer extreme reactions. Zooplus do a really good range of inexpensive valerian toys your boy might enjoy.
(it is also an excuse for more new toys, from his perspective, so everyone wins....
)