I got it working for me in Mavericks with internal display closed (really closed, not just sleeping), but with the lid open (or closed, stays shut either way)
Here's what I did:
1. Enter this into the terminal:
Code:
sudo nvram boot-args="iog=0x0"
2. Restart
3. Log in.
4. Connect a bluetooth device like a mouse.
5. Close the lid. The external display should power off too.
6. Move the mouse. This should wake up the external display but not the internal one.
7. Voila. The internal display stays shut even when you open the lid, while the external display keeps running.
I use this because my aging Macbook Pro's display doesn't work anymore so I don't want the graphics card powering it up along with the external one. I've noticed that this approach significantly reduces the temperature compared to when the GPU was having to power up both displays and the fans were at 6000rpm nonstop, even when I wasn't doing anything. They are nice and quiet now.
To undo the terminal command, just zap the PRAM.