All you would need to do is set the laptop next to said monitor, then connect them with some cable, VGA, DVI, HDMI, what ever your fancy, then right click on the desktop and depending on your OS select personalize or properties and go to the display settings and you can choose your options there. The nVidia control panel can also do it and probably ATI's setup could as well. You can extend the monitor or set primary etc.
You would need to do this every time you wanted to use the monitor I believe.