Quite probably he can - but for the period of time you are watching his aerobatics as an interested passenger, you are not a student - so make sure you aren't paying for that portion of the flight as otherwise he'd probably be acting outside the privileges of his FI rating.
He must also be in 3/90 'recency' if you are going to be a passenger rather than a crew member for that part of the flight.
Tell the tight-fisted git to have the restriction removed!