Customer needs advice about budgeting and billing

I’m a tiny startup with a cute $10 product that a giant government agency suddenly might want to buy a half a million of. My friend, an industrial designer, spent about 50 hours doing designs and mockups, all of which are beautiful and necessary. My other friend, a video producer, did about 50 hours of production design and shooting to make slick videos that were part of the proposal. I have offered generous pay for the time, including a bonus for carrying it until (or if ever) we win that government deal or my enterprise gets capitalized. The video guy is content. The design guy isn’t. He doesn’t want the pay, but wants a royalty on each gizmo sold. The investors hate that, indicate they won’t invest if the entrepreneur has already promised revenue “off the top” to people. I feel like the golden goose here. What do I do?