Airlines short leasing off other airlines do pay silly ad-hoc rates! Longer term leases are still expensive but are negotiable.
Most american B767/A330 operators do not have 180 EDTO approvals, they can get away for the majority of their operations at 120 EDTO to get to Europe.
EDTO is quite conservative and tied to tail specific airframes, airline operations procedures and crew training so it is not easy to move a tail into an operation quickly.
The main issue would be to find a tail that has similar weight specification to be able to operate the sector. The Air NZ B767-300 has a much higher TOW than the QF B767-300 which can be a huge limitation on available range. While I am not familiar with the A330 I am sure that the TOW would be the same differences between tails/fleets. No point paying for a TOW weight you don't need.
Another issue could be catering set up, if your operation uses non-standard equipment set up or the leased aircraft is non standard then up then you also have to arrange lease of special catering gear.