Effectively no. You cannot definitely purchase an upgrade using anything other than cash. You can waitlist a miles+cash upgrade on a UA operated segment that mightclear, or might not, or might be available at purchase. This is an art you would want to learn and practice before investing any faith in it as a means of flying J, and keep in mind that deep discount fare classes incur (IIRC, I can't find the chart anymore) a $600 per direction copay in addition to the miles. As ANZ is one of the last regions in the world to see reasonable J fares, this could still be attractive versus buying outright, but it still likely to be expensive. And actually confirming an upgrade requires a substantial amount of research and expertise.

Technically yes (mentioned above), but in realistic life no. You would require confirmed B space (very expensive) and available I space (virtually nonexistent) on the NZ flight.