I found this advertisement in an Air New Zealand in-flight magazine. Haven't tried it out myself, but seems that if you mention that you've seen the ad (and where), they'll give you a complimentary coffee. Worth a shot, and I would try myself, but don't go to Ponsonby very often.
78 Mackelvie Street
Ponsonby
Nice spotting. A long way from here, but it does seem like a good way to know how many people are actually reading the ad and taking note of it.