Shortcut to grab scrollbar handle

I have a wide monitor, and instead of moving to the scrollbar and grabbing the scroll handle, I would like to assign one of the mouse buttons that will grab the scroll handle. From there, mouse movement will move the scroll handle until the mouse button is released.

Alternatively, a keyboard combination would work as well ... for me, a left handed combination since my mouse is on the right.

Does something like this exist? I haven't seen any discussion of such a feature.