Leaflets in all the backpackers with discounted tickets or something. Must be a few thousand backpackers in Wellington at any moment, many would be football fans. Just need to sell them on the YF experience.
I'm not sure if above has been tried by Nix, or even YF themselves before?
Lots of tourists go to a Super Rugby or ABs game, because they hear rugby is NZ's national game, and kiwis are "passionate" about the sport.
So off they go to watch a game, maybe in their brand new $150 ABs jersey. But the whole experience is a bit disappointing. The crowd is a bunch of mutes, the rules of rugby are very complicated, the endless reset scrums means not much can happen for minutes on end & if mid winter it can be freezing cold. So the highlight is doing a few Mexican waves, to cure the boredom. $50 + ABs jersey for that.
Alternatively the YF in summer offer a fun time (more similar to their football fans back home), and mostly warmer weather. And because the backpacker/tourist is only in town for one game, sort of irrelevant if the Nix are winning or not. Let them take in their Mexican drum, Argentinian flag, Preston North End football banner or whatever - and give them a good fun afternoon/night out.
Offer them free transport (with ticket to the game), via a Nix blazoned mini van which runs around all the hostels/hotels, doing door to door pick ups & drop offs.