Two monitor setup when you temporarily only have one?

[timread]

I have a small portable (Sony Vaio TX2XP) and have set up X using Xinerama to work with an external 19 TFT monitors and it is great. The problem is that when I am on a trip and only use the portables built in monitor, X still thinks there are two monitors and some applications (windows) appear where the external monitor should be, and I cannot access them.

I know that I can copy over my old version of xorg.conf and restart X to get around the problem, but it is a real pain...

Is there some command I can run to let X know that I don't have the external monitor plugged in.

Thanks,

Tim