I'm still playing with this, but figured I'd post it so others can see it, comment, improve, whatever. This is a CC macro that I have used on the fly when my main is a little too preoccupied and can't pre-target the mobs for the CCing toon. It isn't fool proof but here it is.
This is based on setting my MT as the focus and everyone assisting the focus.

/assist focus
/targetenemy (like pressing Tab to scroll nearest enemy)
/cast *CC Spell*

This macro is very conditional. It relies on the focus having more than 1 mob attacking them and the CCing toon to be in close proximity of the focus. (did that make sense :? )

This is semi-reliable and does fail sometimes, but I'm still tweeking it.