I wholeheartedly agree about avoiding security at HNL however possible. The Interisland Terminal is indeed a separate building, but unlike at EWR or JFK, you can transfer between terminals while remaining in the secure area if you check your bags through so you don't have to claim them. Your airline should be able to check your bags through to your final destination without any problem if you give them both flight numbers and the destinations; we did this on our return from Kauai in 2003 (LIH to HNL on Hawaiian, then HNL to EWR to DCA on Continental). The WikiWiki bus that was mentioned before is the way to go. Since you are going TO Hawaii, you don't need to worry about the agriculture checkpoint on the way out there. Instead, simply take your carry-ons, follow the signs for the WikiWiki bus, and ride that to the Interisland Terminal.

On the way back, the process is a little different due to the agriculture thing. Once again, get your bags checked all the way through. When you board the flight on the other island, you will have to run your checked bag through the agriculture screening there and they will put a sticker on it. You do NOT run your carry-on baggage through the ag checkpoint, however. Instead, when you get to HNL you again follow the signs to the WikiWiki bus, and before you board the bus there is an ag checkpoint. They will put a sticker on your bag there. Just follow their instructions and you should be fine; they were much more courteous than the TSA (who in our experience were major-league pricks at HNL).

To give you a further incentive to stay inside security, consider this: When we went out there, we flew into HNL and spent two and a half days there before taking a 35-minute flight to Lihue. The wait to clear security at the Interisland Terminal was an hour and a half. There were a grand total of two checkpoints with two metal detectors each. Avoid it if at all possible!