Have you tried one of the vacation package sites?
www.unitedvacations.com
or Escapes on United.com
or Packages on Expedia/Travelocity/AA.com
UnitedVacations is nice in that you can get the hotel/car for fewer days than the number of days your on-island, if need be.
In April I booked my wife (on two week's notice) KOA-SFO on UnitedVacations.com and the price was 1/2 the same flights booked on United.com! (Had to had one day of hotel for an extra $30, but total price was still ~50% of booking the flights alone through the airline's website)