I can't answer your question exactly, but I can give you hope.
I used to have an Insight EX/NAVI, and now I have a CR-Z/NAVI. Both come with USB, and both have the same head unit. Of course it would be different from the base model. This test was on the CR-Z.
I have a FrankenPre, which is an ATT Pre2, with Sprint comm boards and modified software. With nothing hooked to the USB port, the screen displays NO DATA. If I plug in the Pre it will say LOAD, but not ever do anything except charge. Then, if I select USB Mode on the Pre, it will read the music from the USB. It took some time to read the USB drive, but it eventually came up.
It read from an album in the ROOT of the drive which were .mp3 songs, it read from the Ringtones folder which was all .mp3, and it read from a custom named folder with .m4a songs on it.
There many kits available, and I don't know the differences. I'm sure you could do it yourself based on the kit that Honda sells, which comes with instructions that you can even review online.
Honda Insight Accessories - Genuine 2010-2011 Honda Insight Hybrid Accessories Shipped at Discount Prices
The kit seems a tad expensive, but it is blessed by Honda so that provides a comfort zone. I see "what appears to be" the same kit on eBay for about a third of that price.
I'm glad that you are ludicrously excited. I'm ludicrously excited that I have a Pre3 coming that should arrive this afternoon.