What I found helpful is to IWT with the melee (driving with the healer) and then hit a movement key to stop the IWT when the melee get close enough to aggro the intended target. That way they stop short and are already autoattacking when the mob comes within melee range.

Also, another tactic I have used when trying to avoid aggroing other mobs near the intended target, I IWT with the melee, stop in range of Death Grip and DG the target with one of the DK's. This obviously doesn't work for Paladins or warriors.