I would review the ALPA jumpseat website for current HA info. A couple things changed there recently and I'd have saved myself a bit of stress had I checked.
But the short story: HA in HNL: set up for JS airside at the customer service desk in the interisland terminal. At one of the outer island stations: ticket counter. Listing: not required but appears to be appreciated. Call Hawaiian central reservations. About what moonwolf said... if they set you up for a later flight, you can thank them and then go to the gate and try to hop on an earlier one. That usually works.
Island Air: I tried to catch a ride when it looked like I'd miss two flights in a row on HA (other pilots commuting). The agent turned me away after I showed up :35 prior and the didn't know what to do.... at :31 prior she said 'well, sorry you're too late, the deadline is :30 prior to departure'
As there was no way to get the crew's attention, I hoofed it back to Hawaiian.