I concur with luckydog. As they are simply the domestic leg of an International flight, seating can be made by ringing QF Res.
For those of us lucky enough to have Plat status, the upside is access to the F lounge (rather than the normal QC). The downside is having to go through C&I and give up your BP. The trick is to detatch the stub (to ensure that if the flight doesn't post to your account, you can prove passage), as the main part of the BP will have the orange D sticker (denoting you are a domestic pax on the international flight).