Hi Amy,
I've been trawling through the NZIS site for any hint of a way that you can continue to work beyond the 12 months granted under the visa. So far I keep coming up against the same brick wall i.e. you can't. They emphasise that you are supposed to be entering NZ in holiday mode rather than work mode so it's difficult to justify wanting to work the full 23 months (in their eyes). It's quite something to be able to support yourselves for the remaining 11 months without working though so I don't know how others manage.
The only way I see around it is if you took jobs on a cash-in-hand basis, but far beit for me to suggest you do something illegal

. I'm only assuming, but I guess they keep a track of what you're up to workwise by getting employers to submit details of your visa when you start work with them. You'd know better than me whether your employers have asked for these details. I hope someone can come with some advice from personal experience.