Remember, too, that FF miles that are EARNED often don't show up on your ACCOUNT for another 2-3 months.
If you're buying, it's better to buy the interisland flights EARLY as the price goes up as the flight fills. Could you buy tickets that are refundable (not sure if this is available or worth the price?) and get refunds if you do get seats?
Almost everytime I've gotten NWA FF tickets for interisland flights, I had to use "Rule Buster" which burned 15,000 miles per oneway segment. Ouch. Only use that if you have miles to burn.
A friend was looking for July and couldn't get a FF seat with 3 different FF programs for the Interisland flights.