You should be able to use the standard extension sensor button methods for accessing the wand button data.
From the
Sensor basics documentation page:
Code:
<extSensor>.buttonState() - Get the state of the buttons as a bit flag.
<extSensor>.buttonCount() - Get the number of buttons on sensor.
<extSensor>.isButtonDown(button) - Returns whether the specified button is currently down.
viz.SENSOR_DOWN_EVENT - Called when a sensor button is pressed.
viz.SENSOR_UP_EVENT - Called when a sensor button is released.