LOL fair play. Even so, being defensive is usually a bad move in the amatuers, unless you're VERY good at it. You're better off letting them be aggressive as long as it's not wild haymakers that will get them countered badly.
Put him in with someone and say jab only for him, that will get him on the ddefensive. You could also put him in sparring and allow him a limited number of punches- will make him think.