I use a seperate button/macro for each mage on my team to sheep.
This lets me A) Assign a mark (lucky charm) to each mob on my main while the alt mage /focus's and B) lets me easily resheep any that break early without having them all resheep all the mobs (if I have up to 3 sheeps at a time).

I don't know if I'll contiune to use this, but it works just fine for the instances I'm running currently. Having the lucky charms up helps me determine who's broke early/needs resheeping.