That's similar to a trick in DND. This idea was used by Jolly Blackburn in his Knights Of THe Dinner Table comic. http:\\www.kenzerco.com\
The party defeated a female Owl-Bear. She was guarding her eggs. Teflon Billy (aka Brian) decided to keep the eggs. He looked after them and kept them warm and they hatched into baby Owl-Bears. He kept them in cages, keeping them happy and healthy. He bred them to create even more Owl-Bears. Then when they were just past their prime, he stabbed them mercilessly with a spear while they were still caged. 8000 expeience points per Owl-Bear!
Could you use the Cage spell on a Conjurer monster and simply pick off his summonings one by one?