Hi there!
I'm just posting a little trick I found yesterday evening when on Instructor Razuvious in Naxx25.
This trick is quite simple, but if you have some problems with healing the MC'd adds, it could be helpful.
Requirements:
-Rune Tap
-Glyph of Rune Tap
-Person who MC's an add being in your group (not raid)
Here it goes:
When a player is in your group and is MCing an add to tank the Instructor, just use Rune Tap. What it does, is that it heals these guys for 10% of their maximum health. They do actually have a lot of HP, meaning you could heal them for quite a lot damage.
It's surely working as intended, but it's quite helpful if you got some problems with him.