You'll always have SOME mixing, but it's not going to be enough to worry about.
If you are really worried, with the cap open, give the neck of the bottle a good hit against the heel of your hand. With the right amount of force, the beer will foam just enough to cover the top of the bottle. Re-cap on the foam and you can be sure that all the air is evacuated. Rinse the necks of all the bottles in warm water afterward to clean up any drips.
They do the same thing in commercial bottling lines with a high-pressure jet of water. You can get the same results with a sharp tap.
You know, or just burp them and don't worry about it. :cross: