I am developing a piece of software that is eventually going to run on ChromeOS and will come in the form of an Android app (apk package). We have been asked to come up with a distrubution system that is both offline and simple for this app. I've been thinking about distributing the apk on USB drives and I would like to find a way to get the apk copied automatically to the system when the usb drive is inserted. Updates for the apk could also come later on and they would be on their own USB stick with the same system in order to update the software. Right now, I have no idea about ChromeOS and/or how to do this, I'm in a research phase.
Brute force solution: emulate a USB keyboard to send the necessary commands. (You should require the user to enable developer mode and get to a specific starting condition so you know which keystrokes are required.)
You wouldn't be the first to use a fake keyboard to help with Chromebook deployment. See for example the Centipede. You could combine the keyboard and storage in a single usb stick, also acting as a USB hub to allow it to have multiple device IDs.