May I ask why you want to do this?
If you want to use the device in clamshell mode (where the lid is closed but the laptop is fully functioning), you will have to follow the instructions here:
http://support.apple.com/kb/HT3131?viewlocale=en_US&locale=en_US
On the other hand, if you aren't doing that, then i don't see the point. I'm guessing you want to use clamshell mode.