Have them play toward a portable carpet square. It won't do a TON but it may block out *some* of the sound.

Also, with your current setup, you can easily put them on the third row between your saxes and bassoons, if your horns are on the outside. Move the clarinets up to balance the numbers.

Finally - don't put them in the center. Bounce the sound off the side walls and let it resonate, rather than aim directly at a judge.