I´m not an expert on the area, and have in truth never boxed mages, but I was thinking a little about it the other day since shamans will have hex in the x-pac

What if you wrote a cast sequence macro with commas the same way that shamans do for totems?
Something like this:
/assist [target=focus, exists]
/castsequence [nomodifier] reset=8 Polymorph,,,

Polymorph,,, on your first mage
,Polymorph,, on your second and so on

Would targeting a mob and pressing the button once, and targeting another mob and pressing it again work?
It´s the only thing I managed to come up with at least ;P