First things first, yes this is a "repost" but my way is a 100 times simpler to execute, and I also made a video showing how its done.
>Badly Explained ex.
>Hardest way ever to replicate
1. Go to Stormwind Pandaria portal
2. Target the dummy
3. Have a mount somewhere on your bar so you can see when you want to click the portal
4. Use Storm, Earth and Fire
5. Click on the portal when mount button "glows" up (You have to lose the Buff but still be transformed when getting the loading screen)
6. If done corretly you will stay as the Spirit
A side note: if you still have the Storm, Earth and Fire buff when you get through the portal to Pandaria just click on the portal again or redo from step 1.
Video > Storm, Earth and Fire - YouTube