Unfortunately I doubt the auto-updates will work when the add-on's .xpi URL is not stable because it includes uBlock version number. He might be able to workaround that limitation by hosting a stable .xpi URL on a github.io website.
https://github.com/gorhill/uBlock/releases/download/0.8.5.7/...
Mozilla rolls that option into their CFX builder - https://developer.mozilla.org/en-US/Add-ons/SDK/Tools/cfx#cf... - the update file just needs a consistent place to live. I use CloudFront for it.