I don't have an extra seat, but here's an idea to help keep your next one:
Home Depot sells a package of mini bungy cords like these below for $2 or $3.
How about using one of these to keep downward pressure on the seat or cowl?
Permanently attach one end of the bungee somewhere inside the storage compartment, maybe with a zip tie, so it stays put. Attach the other end to the bottom of the seat or cowl. I can't remember if there's anything on the bottom of the cowl to hook to, so you might have to improvise a hook point or drill a hole. Adjust the bungee length so you have to stretch it when attaching it, so the bungee provides constant downward pressure. Even if the cowl comes unlocked and pops up, it should spring right back down. Might not pop back down perfectly locked back in place, but should be better than it flying away altogether.
Thanks everyone! Yeah, drives me crazy, I just have that seat there should the wife want to hop on...normally run high mounts and no pass pegs. I think I rounded one up Rancksta, buit if it falls through Ill pm ya. I'm tired of losing these things, might just toss the trackday bodywork on tail...lol