On my mages, I use the normal assist the leader macros for sheeping, but my sheep button is different for both toons. (f7 on main f8 on the other)

So when i see a group of 3:
select mob 1 >> cast sheep from main toon (F7)

immediately (while casting)

tab to mob 2 >> cast sheep from 2nd account (F8)

Then freeze the 3rd mob in place and proceed to 2-shot him.
Sheeps last a while, so you can take your time picking the next one to kill, or bandage and pot if something went terribly wrong.


BTW: There is an engineering trinket that "sheeps" targets already. If you have some gold to level up engineering, you can try this out on your shamans now. I think the cooldown is just longer.