Maybe try just a regular sponsored visitor visa, to give you more time to accumulate evidence than the visa waiver would allow, but with no proof of relationship needed. I am not sure if the previous denial of a visa will affect things, but this is the route I took, at the instruction of my LIA.
When I moved to NZ (from the US), my partner and I had been in a long distance relationship. We had actually never even met in person!
He sponsored me for a visitor visa, agreeing to support me financially and pay to send me home before my visa expired. I made it very clear to INZ upfront that I was looking to check both him and NZ out, to see if I wanted to make it a permanent deal. My visa was granted for six months.
As soon as I arrived (as in the next day), he added me to all his bills: phone, electric, internet. He owns our home outright, so we could not provide a joint tenancy agreement. We also opened a joint bank account, which we used to pay for all our expenses. (You need to find one that allows you to open an account on a visitor visa.) Everything we did, was with a mind to show proof of the relationship's integrity. We travelled to see his family a couple times, and we kept boarding passes, receipts, took group pictures with them, even had them mail an invitation to both of us when we went for his sister's birthday. The evidence from each trip was put in its own envelope, and labelled with the dates and event.
After 4 months together, with a solid 3-4 months of bills and bank statements to show, I applied for the partner work visa. I included a timeline of our relationship, all our evidence, a reference letter from his sister and one from his best friend. My visa was granted with no issues.
After we had been living together for a year, I applied for residence. I had kept accumulating evidence, and submitted it all (old and new) along with two new letters vouching for our sustained relationship. Residence was granted no problem.
Like I said, I am not sure it would work for you. I might be inclined to ask your LIA. They're supposed to know what's best.
Good luck!