Handling for external storage like S3

[megamisan]

This look great and I have not tested it yet.

I would like to put a highlight on processing for files on external storage, like a public AWS S3 bucket. I checked if there is a way to replicate the rewrite rule in case of missing file, and it exists (see How to Page redirect (on aws). However, the matching mechanism may not work, since it is not the same domain.
Could a way to catch that implemented? Maybe an URL prefix added in the storage specification? Which can be used in the rewrite rule on the storage and enabling url matching in queue?