You could also use a magnetic reach tool on the screw in the center to pull the plug up if you don't like turning things over. Flipping it quickly after loosening the screw up is quick and dirty, though. You aren't the first to have the thing slide down, we all experience this one from time to time, just one thing about the modern threadless fork and stem set up to handle. No sweat or shame, you write it up to experience and then help someone else in the future when they find this out. Part of bicycling.

Bill