Also, Z has a completely different method for FlyBuys points accrual (
https://www.flybuys.co.nz/Pages/Participants/z-193):
Points collection rate
Every time you reach 20 litres you’ll get a point, no matter how much you put in or how often you fill.
In order to gain 1 Airpoints Dollars, you'll need 5.95 FlyBuys points, which means 119 Litres of fuel.
Assuming ~$2/l for 91, that means spending ~$238 to gain 1 APD, double that for 2.
Currently the quickest way to get 2 APD, is if you successfully apply for an AirNZ Airpoints Platinum MasterCard (
by Kiwibank, before 31st Dec. 2014), then simply spend $75 to get 2 APD (normally 1APD per $75).
But seeing as you don't normally reside in NZ, this option is not practical or suitable for you.