I've tried this with a few friends, and the trick is to keep Omen moving along with as many movement-impairing effects up on him as possible. We had a mage there slinging Frostbolts at him, a shaman shocking him with Frost Shock, and of course a hunter laying down his Concussive Shots and Frost Traps. I was there on my warrior issuing the occasional Taunt just in case one of the DPS made a mistake and got too close (this was never a problem).
After a while, I think it took us about 30 minutes (although we did take our dear time), we got him down to the gates of Orgrimmar. For some reason the Orgrimmar guards didn't like us to well. It might have been because we brought this gigantic dog to their doorsteps, or because we were Alliance and they thought we might grab our swords and fight the Horde. Either way, we high tailed it out to a safe distance and let them take care Omen for us.
A fun adventure had by all! Many thanks to Zentax on the Frostmourne US server, who took the picture at the top of the post when someone kited Omen on his server. And if you've got a couple minutes, check out this neat YouTube video we covered last year of him being kited around.
I've heard that some classes can kite him down to Orgrimmar by themselves, though I haven't seen anyone doing it just yet. Anyone else heard this? What are your experiences kiting Omen half way across the western kingdom?