Hi Laura. I've been trying to figure out this option too. From what I can understand, officially you don't have to work in NZ, or even go there to then use the trans-tasman agreement to get your Aus registration. However, I have been advised recently by some recruitment agents here in Aus that whilst a couple of years ago this was quite straighforward, the APC are now quite aware that lots of people are using the trans-tasman option to avoid the Aus reg process, and therefore have been known to demand that you still take the APC exams etc even with NZ reg... which means you (or your partner) would go through all the NZ paperwork etc (there is a LOT of paperwork for NZ) for nothing.
But if you have the option to go via NZ and do a short period of locum work there first, it should be no problem. However, some people have gone directly to Aus and it worked ok for them. So hard to know - but sounds like now this is not guaranteed.
I haven't been able to get any official answers from the APC on this though..so just trying to figure it out!!
Good luck
Emma