How do I use only the external display with my MacBook Pro lid open on Lion?

I've taken up olivier's suggestion to arrange my monitors to eliminate a common border:

I chose the bottom right because I keep my dock on the left hand side of my screen, and I use my upper right as a hot corner to sleep the display. I also moved the menu bar to my desktop monitor and the MacBook screen is completely dimmed.

There was another option I heard about: using a magnet to make your MacBook think that the lid was closed. This does work - I placed a snippet of a refrigerator magnet near the bottom left side of my keyboard and sure enough my MacBook thought I had closed the display. Unfortunately, Mac OS X also disables keyboard and trackpad input when it thinks the display is closed, so this option didn't work for me.

Mac OS X Hints has discovered a command that will allow this:

To go back to pre-Lion behaviour enter the following command in Terminal:

sudo nvram boot-args="iog=0x0" 

To undo this change type type the following command or zap the PRAM (press Cmd+Opt+p+r at power up):

sudo nvram -d boot-args 

Quick WorkAround (Not an actual solution)

Just check the option "Mirror Displays" in Display Preferences. See below screenshot.

Then turn down the Macbook's brightness to zero.