I think 2-3 people have said they use targetlasttarget macros.

So they target their CC target, then target their kill target, then they press macro that uses targetlastarget -> Polymorph then they use their dps button to assist leader -> frostbolt.
This breaks when they change to a 3rd target since the last target would then be the kill target not the CC target (killing the kill target or changing who they attack).
Could probably be fixed by having a manual button that does "targetlasttarget -> assist leader" when changing target, so the CC target is still the last target instead of the old kill target.
Not sure how well this would work but I think it would work fine.

Some have the ability on round robin and assist leader with just the CC character. (saw a video of priest + 4 warlocks sending voidwalkers to tank individual targets by targetting them then pressing key to assist and petattack, this would be the same thing)
I don't know how he managed to make it work so well, I have a delay on assist so they get my last target if I press so fast, but it looked like he changed target 4 times in <2 seconds and voidwalkers all went on correct target.
I need to wait 1 second or they get my last target with 39ms latency, so idk really how it worked so well for that person.