How can i implement middle-mouse-click on a scrollbar (like in Linux)

macOS lets you choose between actions for clicking in the scrollbar.
I'd like to have both, like Linux does:
left-click: scroll up/down
middle-click: scroll-to-here
Can't figure out how to do it though. Don't see a trigger like 'middle-click in the scrollbar'. Would be fine with a combo of modifier keys, but can't see how to qualify the click as occurring in a scrollbar.
Any clues?
Thanks in advance.