Tonight I found a very easy way to pass the forth boss in UBRS CM, probably heroic also.
What you need:
-good ranged dps.
-know tacts (ofc)
-someone that can dispell enrage
-tank with some ranged spell (optional, makes it faster).
So, the main thing is that you can dps the boss without entering the bridge. Just stay before the door, you can hit him even if it closes.
Phase 1 (just boss): let the tank pull it to make some aggro, then the ranged dps start and nuke him. Avoid the breath and the fire on the ground.
Phase 2 (adds): when adds come they will come in your room. Make sure the tank picks them up and aoe them down.
Phase 3: after second wave of adds the boss will land on the bridge. You can stil hit him, but dispell the enrage since the fire on the ground will hurt if it reaches many stacks.
We did this tonight on EU realms at 4-5 AM.
Bonus tips on second boss:
We tried a funny tact on second boss that worked very well. You need one dps that can go tank and two ranged. Place the healer, the ranged dps and the other tank upstairs. Main tank takes the adds, dps nuke them and the second tank taunts the boss on the stairs. It will take him a lot to get up and kill the others. When it gets up, the main tank taunts back the boss, downstairs. I found this very easy in cm since the boss hits me like a truck (guardian 635 ilvl). You just ping pong the boss through taunts and he won't melee anyone, worked like a charm. Ranged dps intrerupt it and... that's all! This one is more like a guide, but I still think it's not intended.
I hope it helps! Good luck!