UPDATE: It seems that using Duplicate Mode thru the USB-B interface does work. I believe the “trick” is to start a duplicate mode print thru the touchscreen interface. After that, you can run additional duplicate mode print jobs thru the Octoprint, and have them work. I have not really tested this rigorously, but that is my suspicion.
In other news, user @jbot has started a thread about sideloading a VNC server on the touchscreen, and using it to control the J1 remotely: Printer malfunction and exploring touch screen android
I have not played with it yet, but it looks like just what I was asking for!