How to start App Expose without using Force Touch or the keyboard?

I know there was a way to trigger App Expose, by pointing the mouse cursor over an dock icon, and scrolling the mouse wheel. As far as I remember, it was something I had to enable with the "defaults" command in Terminal. Unfortunately I don't remember how to enable this feature, and I can't find it on google nor on AskDifferent. Could somebody point me to the right direction?