Wouldnt it easiest to operate bubble flights out of the domestic terminals ? Realistically only airports which need separation are SYD/MEL/BNE/AKL (Maybe PER if they join). (I know HBA / ADL / CBR operate a few internationals but not many and are single terminal anyway)
Considering neither AU or NZ domestic flights require international security standards, why bother for bubble. Just have a few passport readers and limited bio-security, shouldnt be a huge issue for trans tasman.