Interestingly enough, NZIS have been known to accept home videos too. I know a Kiwi who's partner was English, and they didn't really have the joint bank account etc (which is always cast iron proof to them at least), so they submitted a pile of video tapes of them on holiday together, and that seemed to do the trick. Apparently a letter outlining your intentions in regards to your relationship is helpful too. Okay, it's not official evidence, but it can't hurt to tug at the heart strings - immigration officers are human too!