I recently had a very interesting idea. If anyone has read the 12 month diaper training program, this is a variation. The principles behind it are simple classical conditioning. Associate urination with diapers easy. Taking it in another direction, what if you played a song or some other noise while urinating? I think this might work because classical conditioning has been proven to have effects in thins we have no control over, things like our immune systems.
So a person would play a noise before and during Urination, don't even need a diaper. Eventually the conditioning will get to the point where you begin to urinate automatically whenever you hear the sound. Make sure you pick a sound that you will never hear outside your own house though.