How to boot Macbook Pro when in closed clamshell mode without the windows getting resized
With my 2007 MBP I can get it out of sleep by clicking a mouse button or key on my external keyboard with the lid closed. No problem. 

On a cold boot, I press the power button and then close the lid as fast as I can, and then it boots up on the external monitor with no ill effects.

Should work that way for any MBP!