Anyway to block spells being cast on my mercenary?

Title says it all. Is there any way to block unwanted spells on my mercenary? For example, I just learned about blocking certain healing spells so merc healers don't cast Complete Heal. That's all well and good for me. My merc tank still gets CH cast on them. Is there anyway to block spells that land on my mercenary?

As far as I can tell there is not. The option on my merc is greyed out as well.

No.

But, I wish you could make your mercs cast certain spells. (Ward of the Reverent)

Not currently, but that is a feature I asked for in a feedback thread during RoF beta. One of the developers did respond stating it would be looked in to, but that's the last I heard.

That would be nice. I wish they weren't limited to 15 buffs.

My tank merc doesn't need mana regen, and my wizard merc doesn't need melee haste.
It'd be a great benefit to be able to block spells on mercs. Come on, make a logical change!