We played a very similar format in Fort Collins (Colorado, USA). We would have a 3-hour 4 vs 4 tournament. We would then make teams of 3 players, usually a forward, a back and a newer player. Combining teams of 3 we end up with 2 subs per team.

We would play 15-minute games, combining 2 teams vs 2 teams. The seating teams would help ref / time keep.

After playing all possible combinations we would rank the 3-player teams and we would have a final game: 1st and 4th versus 2nd and 3rd. The final game usually was very even matched and fun.

Jorge