This method doesn't mean you'll be able to level from 80-85 or use the Goblin/Worgen zones on launch, but it means you'll be able to play without installing anything.
1. Make sure World of Warcraft and/or the launcher and background downloader are completely closed.
2. Open up your World of Warcraft folder.
3. Open Launcher.wtf in Notepad and change the "accountType" line from LK to CT.
4. Open Config.wtf in Notepad and change the "accountType" line from LK to CT.
Apparently Blizzard are fine with this. You'll still need to buy either online or a physical copy of the disk to access the extra stuff though.
The additional d/l is 700mb give or take atm.
