Connecting 2 Photons with USB

I am trying to get one Photon to send data to another Photon (with a USB shield) over USB, like so:

where the left Photon talks to the right Photon, which talks to the computer over serial. I cannot get the left Photon to recognize when the right Photon is trying to ask it for USB enumeration data. can anyone please point me in the correct direction?

The Photon does not support USB Host Mode out the box (yet?).
Currently you'd need to build locally and do what's outlined here

Maybe you ping rac146 and BDub or mdma in that thread, to get more background

Could you also post a link to the shield you got there?