Enabling in X works via:
xinput list # find second mouse id
xinput create-master second
xinput reattach <mouse-id> "second pointer"
and to get rid of it: xinput reattach <mouse-id> 'Virtual core pointer'
xinput remove-master 'second pointer'
Works great for clicking, but keyboard doesn't work in some applications when enabled. Dragging windows might attach them to the wrong cursor and other issues. Playing around with xinput can also crash some apps (libgdk-3 here) or leave you in a state without a keyboard or mouse.