Found on reddit, edited for relevance to us
* Shrine/Mage portal to Stormwind, take lake portal to Hyjal, fly down
* Engineering: Goblin, take the Everlook portal
* Shrine/Mage portal to Ironforge, fly down
* Mage portal to Ancient Dalaran, optional corpse run, fly over
* Shrine portal to Ironforge, long flight up
* Shrine/Mage portal to Stormwind, take lake portal to Twilight Highlands, fly over
* Death Knights, use Archerus
* At Shrine, use NPC Gleep Chatterswitch on Shrine terrace to teleport to Ratchet, fly over
* Shrine/Mage portal to Dalaran, take the Caverns of Time portal in the Violet Citadel
* Shrine/Mage portal to Stormwind, take lake portal to Uldam, fly over
* Engineering: Gnomish, take the Gadgetzan portal
*Shrine/Mage portal to Stormwind, fly down
All the Cataclysm portals should be enabled for all toons after 7.0.3; you no longer need to have completed the starting quests in those zones.
more information here, .
Among other things, suggests using Engineering portals, DK Archerus and Druid Moonglade teleports, and various Dalaran/Stormwind/Orgrimmar teleport items.