You need to be a Qantas Platinum or a One World Emerald to be able to access the F Lounge and be flying on either a QF / JQ flight. (Or be a guest of a WP flying on the same flight as them)

I've done things like JQ35 and QF8 runs numerous times, but it is a larger hassle than simply flying a normal domestic flight, since you do have immi at both ends and you'll need to show ID (so Drivers License or Passport), plus the LAG rules which you don't have with pure dom.

That said, you'll normally be advised if you do book a dom via the int terminals, and typically check in agents are only too happy to want to move you to a normal dom flight on checkin, and it takes some explaining as to why you want to fly out from the international terminal.