Jared at the Onlinetravelreview figured out this obscure loophole today:
http://www.onlinetravelreview.com/20...es-round-trip/
He suggested transferring SPG points to fund a Virgin account, but you'll see in the notes that I think it's a better deal to fund the account with AMEX Membership Rewards points (and you can usually get an AMEX card with a high sign-up bonus pretty easily if you need one).
I just want to see how this works in practice, and make sure there are no crazy fees (as you may know, foreign airlines sometimes impose crazy redemption fees).
But if it works, this is probably THE BEST way to book an interisland ticket, given the current nose-bleed fares.
I don't think Virgin offers one-way awards, but we'll have to wait for details on this. Also, I don't know if you could book two HA segments, instead of an actual roundtrip. Like say you're flying from the Mainland into HNL, and leaving for the mainland from KOA, and you want to fly HNL-OGG, stop, and then fly OGG-KOA for 6000 Virgin miles.
All in all, a very interesting development. If there are no redemption fees, everyone in Hawaii should max out the AMEX sign-up bonuses!
EDIT: Jared did some more checking and, indeed, there are NO redemption fees associated with this reward (you have to pay the small TSA fee). You can also apparently take any 2 HA flights (no need to do an actual roundtrip). This is an extraordinary deal for anyone with access to AMEX Membership Rewards points (pretty much any American eligible for a credit card) and a need for 2 interisland flights.