Disable external monitor

[asdf542]

I have an iMac that I keep connected to an LG HDTV via Mini-Displayport to HDMI. I was wondering if there was any way to disable the external monitor without unplugging it? Turning off the TV doesn't actually disable the monitor as I still have the OS thinking it's still on therefore spaces imitates it as being two monitors when its really only one. The main reason I want to disable it is to save my VRAM while I'm playing Source games on Steam.

 

[Hellhammer]

SwitchResX

 

[hawaiiken]

Tried SwitchResX, doesn't help. The only way is to unplug my Mini DisplayPort to HDMI adapter every time I want to turn off extended display. Wish Apple would provide a simple "Turn off extended display mode" menu option.