I agree with Dave that using a queen excluder in this way is a mistake. It wasn't designed for this purpose and someone who tries this simply hasn't understood the basic principles of modern beekeeping. We try to prevent swarming overall, not on a case by case basis. This means young queens, plenty of room for expansion of brood and honey storage, and probably removing some brood in spring to either start new hives or bolster the weak. Swarming is a hive's response to certain conditions -- mainly a lot of young bees crowding the nest and usually a honey flow. We try to keep them busy in the supers and keep their "minds" off swarming,Some will swarm even so. That's nature's way.

Peter
Ithaca