I've done some structured games on a team ride long in the past, but never an open group ride, and never with more than about 6 people.
*Lead out practice
*The group holding a steady hard pace (like 26mph) and individuals rotating attacking the group and staying out front solo as long as they can.
*Split into two groups, give one group a lead or so then the second group pursues.
Same. TTT simulation can be fun (and hard) but it requires everyone to be on the same page.