I had a horrible time getting Angel to sit there that's why went bribery (older brother's game boy) it was a toy she loved but wasn't allowed to touch unless sitting on the toilet.
unfortunately with a 15yo young man the only forbidden object I can think of is Playboy magazine; then you are going to have a different sort of mess to clean up that you would rather not think about (or how it got on the ceiling? LOL) sorry gotta find humor where ever I can... it's a coping thing.
I know putting a tv in the bathroom is frowned upon in normal parenting circles but here the general rule is do what you have to do to get thru the day. (in other words whatever works)
Nancy