Just toss a circle clip or slightly bent cotter pin into his cockpit. He'll spend weeks worrying about where it came from.

I found one in mine today. Looked everywhere but up the mast. Fortunately my mast was thoroughly inspected on the ground just a few weeks ago by myself and a rigger. I looked for that kind of stuff to be well secured and I assume he did also, as I paid him for a "safety inspection"