I have found that this command in Terminal restores Snow Leopard functionality in Lion to closed-lid/clamshell mode.
1. Open up Terminal in /Applications/Utilities
2. Type the following command: sudo nvram boot-args=’iog=0x0′
3. Press return
4. You will see a warning about using the sudo command. PLEASE make sure you typed the command into Terminal correctly. Mispelling sudo commands can be… dangerous.
5. Type in your password to confirm the command and press return.
6. You should see nothing visible change.
7. Restart your Mac and the Snow Leopard functionality should be restored!
Note: Resetting the PRAM will erase this modification. If you are ever told by Apple to reset the PRAM or need to for another reason, you will have to do these steps again. The mod holds as long as the PRAM is kept intact!