Use pipe insulation from Home Depot on the rails along with the bubblewrap.
^^^ THIS, it's only a couple bucks, get the kind that has a slit cut down the middle already and all you have to do is wrap it around the rails, i even cut off smaller pieces for the nose / tail, then wrapped it in a blanket, taped it up, then put in the travel bag, not one ding from Jet Blue, thought about sending them a letter thanking them.
If you barter or shop before you go, you can get good rental deals. Shops are everywhere on Oahu. I like Local Motion and another small one right in Waikiki. I've rented a long board for $125 for 10 days (soft racks included) in Waikiki. Much better deal than the hastle of packing, negotiating the airport and shipping. You can also buy a beater for not much more and leave it or take it home as a suveneir.
Went last October for 14 days, Bought a board there since i was in need of a new short board and flew it back. Bubble wrap it and for extra support throw cardboard in there. Also save room in your luggage and wrap your towels around the bubble wrap/cardboard.
Definitely take the trip to the north shore - like they've said you'll be surfing with 1/100th of the crowd and if you score it you will remember it forever.