I have my CC spells bound to numpad 7 and 8 (hex on 7, bind elemental on 8 for the shammies)
I do select the target for the CC manually on each char, and walk them into range.
With the tank I select the mob who's going down at first.
Then I press numpad7 to hex those 4 mobs at the same time.
Spam assist button, make sure the dpsers are all targetting the same non-CCed mob, and kill it asap.
Works pretty good so far, annoying big groups in fe VP HC go down in one go.