#OSX Tips & Tricks
Disable the Internal Laptop Display
sudo nvram boot-args="niog=1"
After executing the terminal command, reboot and close the lid immediately. Keep the lid closed during boot up, and once logged in to a user account in OS X, open the lid. If in sleep mode, just close the lid before waking the MacBook Pro and open the lid once again after logging back in.
To undo and return to normal display behavior:
sudo nvram -d boot-args
Similar to prior versions of OS X, resetting the PRAM can also disable the setting.