A bit of a modification on the bag I used for many years would do it. The bag had one main zipper down the middle and would open up like a book rather than dropping things in from the top like most bags.
Add a couple of velcroed tie-downs and remove the outside pocket on the side with the laptop. When you got to x-ray you would simply unzip it and lay it flat on the belt.
I much prefer that bag design, unfortunately it doesn't fit my current machine and I can't find anything like it that does.