One way you can try to get all 30 games played in your event is to make it match play, one vs one. Each round is best 3 out of 5. The first game in the match is randomly selected. The loser of the game gets choice of position or game selection. A player may not select the same game twice until he has played on all 30 games.
With this method, all 30 games are eligible to be selected.
Sounds like a great day of pinball! Good luck to everyone that can attend!
Marcus