You could use a joystick button and wire it directly to the open motor invert terminal.
1) Unbundle the buttons (brown 'out' terminal) on the JoystickGet.vi [this can be done by right clicking on the terminal, most things in LabView can, I've found new love for my right mouse button
]
2) Wire the desired button to the invert terminal on the OpenMotor.vi (2 motors or 4, it doesn't matter)