First find your synaptic configuration file.
Mine was:
/etc/X11/xorg.conf.d/20-thinkpad-trackpoint.conf
And add these lines at the end of the file.
Section "InputClass" Identifier "Trackpoint Wheel Emulation" MatchProduct "TPPS/2 IBM TrackPoint|DualPoint Stick|Synaptics Inc. Composite TouchPad / TrackPoint|ThinkPad USB Keyboard with TrackPoint|USB Trackpoint pointing device|Composite TouchPad / TrackPoint" MatchDevicePath "/dev/input/event*" Option "EmulateWheel" "true" Option "EmulateWheelButton" "2" Option "Emulate3Buttons" "false" Option "XAxisMapping" "6 7" Option "YAxisMapping" "4 5" EndSection
