For this you must be a Warlock with Glyph of Eye of Kil'rog
All you have to do is use the Glyph's effect for your eye of kil'rog to place your portal. Have the eye place it in a corner and sometimes it'll glitch you through a wall, or the floor. I discovered this while running an old instance trying to skip trash, and I would be tossed through the map when I ported to my Demonic Circle. It seems to work quite often in the Gui Lai halls, if you've got an extra Ancient Guo-Lai Cache Key but haven't gotten the required dailies to open some of the phased doors. If a lot of people are not having success with this, I'll delete the thread. Good luck!
1. Place demonic cirle at your feet
2. Summon eye of Kil'rog
3. Have the Eye of Kil'rog place your demonic circle at the corner of an object or wall (you will see that sometimes your Eye will move a few yards in any direction, then it will lay the circle.)
4. Use Demonic Circle: Teleport
Here's some screenies underneath the ground
Attachment 10651Attachment 10652