Enabling middle-click to scroll on ThinkPad T420 touchpad

I have a ThinkPad T420 that has three buttons at the top of the touch pad and a clit mouse pointer stick.

In Ubuntu 16.04, holding the middle button down and moving the pointer stick would simulate a scroll wheel. This was configured by default. However, now I'm using Debian Jessie with GNOME3 and can't figure out how to configure this behavior. The pointer stick works, and the middle button works to close tabs and whatnot, but the scroll-wheel behavior doesn't happen.

I'm sure there's a simple way to fix this, but I haven't been able to find it yet. Any help would be appreciated!