They are already serving access denied replies, so I assume they can identify the browsers via user agent or similar?

If so, returning a bogus file that blocks everything and adding a comment in that list asking the developers to use caching or mirroring the file should be fine.

I wonder if those browsers honor the list when fetching the update though. Would be awesome if you could just add easylist and lock out further requests right on the device.

Everyone in the world is impacted if the site goes down under load. Changing that to everyone in a particular country (perhaps with a given user agent if the free plan allows expressions) would still be an improvement even if other work is needed.