About 35 minutes ago our pally tank had this work in 25m Heroic, stunned the boss in the middle of the room where he was tanking him.
He bubbled right before the knockback and was charged, it ate his bubble but stunned the boss.
"A friend in need is a friend indeed, but a friend with weed is better"
To clarify, ice block before he does his massive crash (BEFORE you get knocked against the wall) then when he hits where you were when you blocked, wow thinks he's hit the wall.
This works to an extent, but not as it's written in the OP and even then it's completely luck-based. If you Bubble/Ice Block right before he casts Massive Crash, you won't get knocked-back. There is a chance that he'll target one of the Paladins or Mages (hopefully in the middle of the room) and charge them, and assuming that they cancel their ability and move away, Icehowl will be stunned where they had previously been immune.
That said, it's fairly useless. You can't guarantee that Icehowl will go after the Immunity classes, and even then all you gain is a boss stunned in the middle of the room. Might be useful if you're attempting Heroic without the speed buff, since presumably he'll be stunned in range of everyone, but this is nigh-impossible to exploit effectively.