Keith,

.....The population builds up and then we have swarms....

To make it less likely the observation hive will swarm, it helps to remove
some field bees.  If you can alter the top level so it is easily detachable
(maybe with 2 slide-in metal plates to give what remains a roof, and to
give a floor to the part you are moving), then you can carry it away even
during open zoo hours, with no bees escaping. Take it when there are many
many bees (but not the queen)on that top frame of honey. Take it to a
beeyard far enough away that they won't fly home, and shake them off.

Anne in NY