zwave.associationV2.associationSet takes in a zwave device id to associate with; however, a device handler can’t have a device input type:
http://docs.smartthings.com/en/latest/ref-docs/device-ref.html#device-ref
(I tried; it almost works and lets me select a device in the preferences, but then instead of getting a Device with which I can get a zwave network id, all I’m given is a [string] uuid of the device that was selected)