Awesome work! I wasn't looking forward to working out all this stuff on my own.
The only problem I've encountered is loading the DFU drivers in windows 7. It seems they aren't signed so win7 refuses to allow access to the device via Flip. I had to install it on an XP machine before I could write my newly compiled .hex to the 8U2.
There are ways of making win7 load unsigned drivers in test mode, but this is cumbersome.