Cooper Accessory Slave
Cooper makes an in-wall switch that is meant to act as a 3-way, or a secondary on-off switch, also known as their accessory dimmer. Pair the device like any normal Z-Wave device. After assigning it to a room on Vera's devices tab, click the '+' button, choose 'Custom Z-Wave Settings', in the 'Group ID:' input box type the number 1 and click 'Add Group'. Then click the 'Set' button to see a list of all other Z-Wave devices and put a check mark next to the In-Wall dimmer or switch that is the master. Click 'Back to ZWave Settings', and click 'Save'.
Now when you press the button on the accessory device it will turn on and off the master switch or dimmer.