Just looked. Between 2005-2009 there was a playoff between last in Central League and a Capital/Central side. Every time the Central League side lost.
None of them were close either:
2005 Stop Out 5 - 2 Red Sox
2006 Team Nak 5 - 2 Red Sox
2007 Petone 10 - 1 Team Naki
2008 Wairarapa 8 - 1 Stop Out
2009 Tawa 8 - 4 Wellington United
2010 Maycenvale 5 - 0 Team Naki