The bottom line on special votes

David Farrer tells us what the special votes can do.
basically
1) National is at risk of loosing 1 seat (reasonably high chance)
2) Labour has a resonable chance to gain or loose one
3) Progressives have a reasonably high chance of gaining one
4) Greens have a small chance of being out of parliment
5) the Maori have a reasonable chance of getting more votes that intrestingly will just result in another party loosing a seat (quirk of the system).
6) NZ first has a tiny chance of gaining a seat

Overall it is VERY unlikely that special votes will alow a centre right government since if labour looses a seat the progressives will get it - if maori party gets another seat it wil probably be at national's expense if NZ first gets one again probably at national's expense.

Only non complicated poption is if greens slip below 5% this depends on how good their organization was this election - I think it was reasonably good so I think that is very unlikely also.