When I've seen this sort of thing done overseas, it normally comes with accommodation, meals and a quite reasonable number of Euros/US dollars per day. I can't imagine why anyone would do it for free, or just costs.
The point Markis and I were working around was the 'why'. As there's unlikely to be any cargo, and Brisbane didn't have any outlandish weather/fuel requirements, then why was the aircraft so heavy that it became performance limited without any headwind. Planning should not be taking wind into account when they sell the seats...as often as not Wellington is very windy, but it's all crosswind, so that does not help at all with the performance calculations. If they NEED the wind to become airborne, then offloads should be reasonably common...unless it's rarely got a decent pax load.