Just looks like an accident waiting to happen. Plus, if you say he only does it if a treat is shown will make him want to search and beg for the treat. And because only you and your cousin handle him, doesn't mean you will always be the only ones ever handling him. What about farriers, veternarians, and trainers? Or even judges at shows (if you attend shows).
But kudos to you and your cousin for teaching him tricks, it's a nice thing to pass the time and go to people and say "look what I can do!" I trained my horse to give kisses. Instead of loping when making the kissy noise he will just put his nose on my face. It's sort of cute, because he always kisses me hello and goodbye. But only when I ask him, and I've never treated him for it. Just more of a habitiual trick that he picked up on after a while.