MacBook Air :: How To Force Single Screen When Flying Blind?

I have an MBA with a busted screen (nothing but gray, though responds to ambient light changes and brightness settings). It boots and everything sounds fine, so I assume its just the screen. I brought it in to the Genius Bar, and they want to send it in under a recent previous repair (liquid damage; they had to do a brain transplant). I was still trying to get everything synced up right before I re-enabled TM with my Time Capsule, so I don't have a backup of the MBA hard drive, and I have to keep those files. And, of course, Apple cannot guarantee the safety of my data.

So... I buy an external HD and some cables and bring it into work to do a bootable HD backup. (I don't have a monitor at home; the MBA was supposed to be a desktop replacement... Yes, I know...) Anyways, I plug the monitor in and get the second screen! The mouse cursor scrolls off to the right onto the second screen and everything, so the system must be fine; it must just be the video.

Now I'm stuck. How do I enable single screen mode? Keep in mind that I'm flying blind on the first screen, so what key sequence would I use to open System Preferences etc. to enable mirroring or whatever?

No, neither I nor work have any USB keyboards so I can't just drive it with the lid closed. I don't even know if keyboard only will work, so I may need a USB splitter to get both a keyboard and mouse on anyways, and neither I nor work have a splitter.