In my recent experience the bag scanners have taken so long to look at each bag on the X-ray that the problem isn't waiting until you can get through the metal detector, it's getting through the metal detector and waiting until your stuff finally catches up with you.

If you see that people are running ahead of bags, as they seem to be lately, put your laptop ahead of your other stuff on the belt.

If you see that bags are running ahead of people, as it traditionally used to be (and which the scam mentioned above assumes) so you have to wait to go through the metal detector, put your laptop on the belt last, behind your other stuff. Then hold onto it until the metal detector is free. You won't be holding anyone up - it's not like they can go through the detector before you do, and you'll go through it as soon as you can.