Using Intel HD or Nvidia proprietary driver

[Clad in Sky]

Hi,

I have a T420 that has Nvidia Optimus graphics. Fortunately, I can also tell the BIOS to use either the integrated Intel HD graphics or Nvidia discrete graphics. When I'm at university, I don't need nvidia graphics but long battery life. At home, I sometimes use the laptop to play Diablo 3, which runs a bit better on the nvidia card.
The Intel HD won't run with a xorg.conf in place, whereas the nvidia card won't work without one. So my question is, can I put both into a xorg.conf and the X-server will use the entry for Intel when the nvidia card is switched off and use the nvidia one when it is on? Or do I need some sort of script that handles that for me?
Now I have a xorg.conf that I rename to xorg.conf.nv every time I've finished using it, so next time I start the computer there won't be a xorg.conf and the intel driver works.
I'm sure there must be a more elegant solution.
I know there is Bumblebee, but switching while the computer runs is not really what I'm after.
_________________
Kali Ma
Now it's autumn of the aeons
Dance with your sword
Now it's time for the harvest

[Gusar]

The simplest is having two config files, then telling X which to use: