Go to the wreckers and get a cut cluster plug (VY or VZ).
Release one of the wire terminals. You will need to lengthen the wire so it reaches the BCM.
Rip out your cluster.
Connect new terminal to #3. This terminal is vacant.
Connect other end to BCM plug X4, terminal #22 (white/green). I used a scotchlok cause I'm lazy.
Works well. Although does light up when the BCM activates the interior lights (e.g. unlocking doors). Big deal!
All terminals mentioned are clearly marked on connectors.
Cluster connector pic below.
Why Holden decided not to wire the door ajar warning I don't know.