With Fursphere's solution, you can also move away from using /assist and then you can CC as well, like so:

Set focus to your Main Assist/Tank, target the mob you wish to CC.

/cast [target=focustarget] pwnmagic
Above for your DPSing needs

/cast Polymorph/Seduce (Don't really need a macro for this)

I use F1-F5 for Focusing, then F6-F9 for making the alts (F6, F7, F8 and F9 are 1 through 4 alts) assist my Main for purposes of setting targets before engaging. Just select the mob you want your alt to target, then hit the hotkey!

I use AHK for this.