1.) Go to the directory C:\ProgramData
2.) Rename the files "Battle.net" and "Blizzard Entertainment" to "Battle.net -backup" and "Blizzard Entertainment -backup"
3.) Go to your World of Warcraft directory (Default: C:\Program Files (x86)\World of Warcraft)
4.) Open the "Temp" folder and delete the file "5.0.4 Migration"
5.) Run the launcher normally
If it worked you will begin downloading "Update Tools" from the Cataclysm launcher, World of Warcraft Setup will launch (Possibly asking for User Account Control) and then the new MoP launcher will open and begin the optimization process.
If it did not work, go back to C:\ProgramData and rename your backup files to their original names.
Let me know how it works or if anyone else has some good suggestions to try.
(On a site note, if / when the optimizer does begin, it is completely normal that it will stay at 0% for an eternity, wait it out and don't stop it, you'll only cause more problems)