RR-80 Remote Schematics
I believe you are correct. I was looking at the same problem myself. I have an intervalometer that is set up for a Canon 5D and I want to cludge an adaptor so I can use it on the XE 1.
I don't know anything about the usb port. Fuji makes a remote (RR-80) that works through the usb port, but they don't provide any information (at least I couldn't find any).
Good luck with your project.