First, there are no boats from Darkshore (Auberdine was destroyed). So I corpse-hopped through Stormwind for an hour to get on the boat to Darnassus, arrived, and their level 85 guards, always on watch, killed me and sent me to a graveyard in...
Since there's no boat in Darkshore, and since I found the hard way that fatigue does kill ghosts running on foot, you almost make it but not quite when you run as a ghost across the ocean.
But it's possible, according to an extremely dedicated person on Wowhead:
i ran up the Darkshore coastline till i was as close as possible to Rutheran Village. Popped my elixir, jumped on my 100% mount and ran across water. You will fatigue but the bar begins to replenish as you get close to Rutheran. Once you hit land you can either take the boat to Exo or run like heck for the portal into Darnassus. You will more than likely die entering the portal or coming out the other side. No worries you will be at the gy in Teldrassil, not back on darkshore. Rez and hit the table in Darn. I then swam via the water channels in Darn to the portal and then jumped on boat and headed to Exo. The tables here are very easy to get to as i did not aggro any guards at any point.As God is my witness, I am going to earn this freakin' turkey pet.