Non-reving inter-island is fairly easy since there are 5 different airlines (Hawaiian, go!mokulele, mokulele airlines, island air, and pacific wings) serving the islands. Hawaiian offers a $49.00 walk-up non-rev fare for any airline employee called the rainbow fare. Mokulele offers a $29.00 walk-up non-rev fare for any airline employee. go! mokulele also offers a non-rev fare which would have to be booked through their pass bureau or reservations. For island air and pacific wings they do not offer walk-up non rev fares, however you can use an ID90 on them.

Ticket prices inter-island have been pretty steady at about $59.00 one way. Since they are so many options it may be worth trying to non-rev. Being an airline employee in Hawaii, I have non-rev between the islands many many times, and I can not recall anytime that I was unable to get to where I wanted to go. If you need more info let me know! Good luck!