Quoth Colin Paul Adams on Pungenday, the 56th of The Aftermath:
P.S. How do I right click (and middle click??) with the mouse in
GNOME on the Air?
If synaptics is enabled, hold down two fingers on the pad while
clicking to simulate a right-click; holding down three fingers
simulates a middle-click.
You can also drag two fingers on the pad to scroll.