I played around with 2 different ways of doing this over the past two days (pulling out my hair in the process…) but I did manage to come up with two working options… Socat-to-socat and usbip.
For the Socat version, I used this fork of homeassistant-socat to build a replacement hassio Docker image with socat inside, then trick the Hass.io installer script into using that image instead of pulling the official. The downside is you need to repeat the process every time you want to update Hass. I couldn’t get socat’s simlinked device to register inside the official container.
My final solution was to use the usbip, which was a P.I.T.A. to get working because I’m trying to go from A Aeotec Stick on an RPi3 (fine, no issues) to a Rock Pi 4B which I had to compile usbip from source because it’s such a new board there isn’t a lot of support behind it yet.
It’s working at the moment…