We found out that it is possible for more than one person to get a cage from a single beast.
All you need to do is stack very tightly and face in the same direction. Everyone set up the trap. Damage the beast enough and have the person with aggro run back. If you stacked well, everyone will get a cage (and you will see the friendly NPC spawned several times).
You do not actually have to be in group, but obviously it makes things easier; it is best done with a tank, so that you know who will have aggro.
Makes things much easier and fasterwe did it in 23 people raid on the elites in Nagrand.