Soft Play (Collusion) in Tournaments

[oscark]

I own a small poker room. We offer almost solely cash games, except for a once weekly tournament.

For the tournament, we have recently had a group of 7 players consistently enter. These guys always soft play as a team. This last week was painful. 5 made it to the final 7. It was obvious they were not going to enter a large pot with one another. Their only goal was to eliminate the other 2.

Let's assume for certain reasons you cannot just ban these 7 from entering the tournament (unfortunately). What would be our best plan of action? What steps should the tournament director take?

Thanks,

Oscar