Hi Polecat,
Welcome to the forum
Without qualifications, there are 2 options. One option is points gained thorugh work experience. You say you've only done mundane jobs, was there anything in there that could be classed as skilled?
The second option is starting/buying a business. This is a bit of an expensive route though, and usually you need some kind of business experience.
There's not many, if any, qualifications you can do in under 3 years that would benefit you points wise. Maybe you could consider a trade qualification, like plumber or electrician? I think they are 2 year courses, and those jobs are also in high demand in NZ.