I haven't actually used flip, so I can't help you - but it is never appropriate, on any forum, to be all "why aren't people helping me there are X many views". The portion of people here who use flip is pretty small, so you're likely to see a fair number of views before you get a useful response. Many people here use clones that don't have the 16u2, or use ICSP to program their AVRs (particularly here in Microcontrollers), hence flip is not relevant to us. The micro doesn't seem to be super popular among the official designs either. Of those that do use boards that can be programmed via flip, few of us do so. Hence, it's no surprise that there would be lots of views with no answer, even if all views were real people.
The arduino team really snatched defeat from the jaws of victory with the whole 16u2 as serial adapter thing. If they'd made the extra pins usable, provided IDE support for programming a 16u2, or even just a facility to upload a few FW versions for HID, just serial, midi, etc, and provided an easier way to load code onto it - it would have been a great idea. Except they didn't, so hardly anyone in arduinoland ever has occasion to change the code on the 16u2, and the 16u2 is a more delicate chip than dedicated serial ICs, and lots of people in arduinoland abuse the boards because arduino is targeted at people without much electrical design experience.
But yeah, point is, you're asking a question that only a few people here can help with.