You can do team preview if you battle through the union room. Is the problem because there are too many players in the union room?
But last year I had 64 players for the convention. I had to turn people away because we were under a tight time schedule. This year we increased the cap to 128 (doubt we will hit that many though)
But yeah, as you can see - the convention is way to large to have it run in the union room.