Press and Hold (long-click) Support for Mouse Gestures
Here's some animations I created to demonstrate how the preview could look:
Long Press followed by Up
Up followed by Long Press
You should be able change the time before it register as a long press.
To make sure that it doesn't read your gestures with long presses when you don't want to, it would just have to check if your attempted gesture had a Long Press with a matching gesture that is saved. If it can't find a match, it would just ignore the Long Press and check if there's a match without a Long Press. So if you don't have any mouse gestures that includes long presses, you wouldn't be impacted by it. And if you're concerned that it would make gestures less responsive, as an experienced programmer I can say for certain that it wouldn't make it any less responsive.