I was thinking a number of different ways to obtain CASA ATPL and this seems to be the easiest way and the most cost effective way as well.
For those holding CASA CPL and 1500 hours total time:
1) Go to U.S, pass FAA IR written, get FAA ATPL concurrently with a a type rating such as B737CL or A320. This will get you a FAA ATP with instrument rating.
2) Go to NZ, pass NZ IR written and NZ ATPL written tests. Rent a Air NZ sim (B737 or A320) and get your ATPL checkride done.
AFAIK, instrument checkride and ATPL checkride can be done concurrently.
3) After you obtain NZ ATPL, convert it to CASA ATPL by just paying a small fee.
For those holding ICAO ATPL and working as a F/O in overseas: (This is what I'm working on)
1) Get 1000 hours SIC time (post-ATPL issuing date) on ATPL issuing state reg aircrafts.
2) Go to NZ and get a ATPL checkride after passing NZ ATPL Air Law.
3) After you obtain NZ ATPL, convert it to CASA ATPL by just paying a small fee.