Why not make this easy Hijacker. Treat this like any other real event listed on here and require registration either through replying here or PM'ing you in game.
You still have the possibility of some jerk looting an ESI and staying quiet, but that would always be the case, and anyone who doesn't register is kill on sight.
Look, I looted an armor part at one of these a while back and I was happy to give Hijacker a 20% share + tip. The guy spends a fair amount of time, money, and energy gathering parts to spawn this thing. Most of the time he just loses his money. His terms aren't selfish or egregious by any means, they're minimal when compared to what it takes to spawn the beast. You only pay out on items, otherwise you keep 100% of the shrapnel etc.
Why this became a 4 page debate and series of questions is beyond me. If you go out to shoot the worm, you pony up 20%, end of story. Otherwise don't go. Simple as that. I think its awesome these guys are doing a public invite, and I'd hate to see it just become a private soc thing.