Treat MacBook screen as monitor even when closed? Background

I have a MacBook Pro running 10.8.3. I have one external monitor plugged in, and the MacBook is largely stationary because it is a work computer.

When I go home for the night, I lock the screen, turn off the monitor, and close the laptop (I often have things running into the evening or overnight, hence no sleep or shutdown). When I arrive in the morning, I open the laptop and turn on the monitor, and all the windows are gathered on the laptop screen.

I'm assuming what happens is that when I close the laptop, the OS decides that only the external monitor is an available display, makes it primary, and moves everything there, and then when the laptop opens it repositions everything to the "new" primary display.

What I Want

I want to be able to close the lid of my laptop, open it again, and have all of my windows be where I left them, all while leaving my external monitor plugged in. Is that possible?
I'm not sure that this is quite the solution that you're looking for, but the utility Stay does make sure that windows return to a set position when connecting an external display. I haven't had a chance to use it myself, but since purchasing a new external display, I must say it's tempted me. 

You might also check out this related thread on .SX, which has more suggestions.

A quick search pulled up this article, which might also solve your question by disabling the sleep signal sent when you close the lid… Someone with stronger terminal-fu than myself might know some direct CLI commands to do this directly.