How do I use only the external display with my MacBook Pro lid open on Lion? Sorry for the wordy title, but my problem is thus:


When I'm at my desk, I would like to use only the external display.
With the nifty gestures in Lion, I have decided I would like to use the internal trackpad on my MacBook
To physically touch the trackpad, the lid on my MacBook Pro needs to be open


This used to be a piece of cake with Snow Leopard and below - you plug in the external display, close the lid, plug in a USB device or press a key on a connected keyboard to wake the machine, and once it's woken up and using the external display reopen the lid and the internal screen stays off.

Unfortunately, Lion detects when my MacBook Pro is open and thinks its being helpful by activating the display. Is there a way to disable that? Is there a way to fool Lion into thinking my lid is closed?
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.