Good point. Walking, battling gym leaders, evolving, very nearly everything you do makes pokemon happier. It'd be hard (or expensive) to make them anything but happy. A held item like that os a good idea. Maybe some sort of anti-haircut too? Like Brutal Training for rocket Pokes?

Is ot possible to make pokemon just not like being on team rocket? Maybe if you are, then walking and such would lower happiness instead of raising it?