I'm not opposed to the gaming idea, but the problem is more about creating an organization with the 'right' to catch them and sentence them to such a fate. What a group ripe for abuse!

Maybe it would be enough for any old Seastead citizen to figure out that their neighbor is a slaver, round up a posse & initiate force against them personally. Or better yet, they could try to smuggle the slaves some weapons to have their own uprising.