I bit the bullet and ordered a Hirose connector from Mouser so that I could get a USB connection into my Zipit and test out this theory.
This is the part: http://www.mouser.com/Search/ProductDetail.aspx?R=ST40X-24S-CV1%2880%29virtualkey64550000virtualkey798-ST40X-24S-CV180

I'm thinking that this is going to be really tough using my current methods.  Because the kernel is a 'sealed up' done-deal, and USB is typically compiled in.  So I will probably have to rebuild the kernel with all USB features attached as modules.  But if all that fails, I could always take the route of flashing a replacement kernel onto the device.

Anyhow, I will post an update in a week+ when I have some progress to report.