Best bet would be to chuck it in at Makara and head up to Boom I guess, although we shot down there a little while ago and couldn't find any decent structure.

EDIT: South of Makara there's a heap of interesting looking stuff on the chart, would be worth an explore in the right weather.

 

Next closest would be around the top and back of Mana, plenty of good structure out there, and maybe the pin/lump off the end of Hongoeka Bay.

 

There's apparently some structure worth jigging over between Puk Bay and that point but it's something you would have to hunt out with a sounder and take GPS marks, I haven't found any yet.

 

On the south coast, maybe Airport Reef, otherwise again it will be uncharted structure you have to hunt for with a sounder.

 

A bit more of a run is the north end of Kapiti, and then the widest (but some would argue the most productive) is Hunter Bank, but that's a bit of a drive in a 12ft boat and you would want to be damn sure it wasn't going to get snotty all of a sudden. I have seen a couple of boats around that size out there, although they were inflatable pontoons so a little bit safer if it all turns to crud.