To enable this permanently:
Create a file with the commands in mikewhatever answer:
echo synclient VertEdgeScroll=1 >> ~/.conf/scroll-touchpad
echo synclient VertTwoFingerScroll=1 >> ~/.conf/scroll-touchpad
We make it executable, and protect it from being deleted:
chmod +x ~/.conf/scroll-touchpad
chmod -w ~/.conf/scroll-touchpad
The we add to our gconf settings this file:
gsettings set org.gnome.settings-daemon.peripherals.input-devices hotplug-command '"'$HOME'/.conf/scroll-touchpad"'
Now you can restart Gnome, log out and in, etc. and your preferences will persist.
(using also Nahuel answer)