Found a very easy way to turn a DK in to an amazing healer on Dreamwalker.
1. Use Control Undead on this guy after killing the Val'Kyr miniboss just before Dreamwalekr. Captain Arnath - NPC - World of Warcraft
2. Spam his Flash Heal and Power Word: Shield ability on her.
3. ????
4. Profit!
Each Flash Heal heals for about 300k, which put me at the same HPS as a fully geared healer with CDs up. Makes for a very easy kill.
Found another use of it, which I used for LK, but can also be used on any other fight.
1. Aggro (they fly around the spire that brings you to LK's room) http://www.wowhead.com/npc=37098
2. Use Control Undead on the illusions that she spawns of yourself or your raid-members.
3. Some extra DPS for any fight past Deathbringer.
You will gain different spells depending on the class you controlled. I got a fury warrior, which got me a Bloodthirst spell and Heroic leap. The bloodthirst did about 30k damage per, which is a decent dps increase. I'm sure different classes work better, haven't others yet.