I need to do some more playing about with this, but via FTP I downloaded an (unplayable) HD recording from the Aura. I then deleted it from the aura itself so it no longer showed in the list of recordings either on the box from the front end or via FTP from the backend.
I then uploaded the downloaded recording, with no changes made to the file name etc, to the "Uploads" directory on the aura's FTP server.
Post upload it was processed by the box, removed from the "uploads" folder, deposited back into the correct ByChannels, BySeries and ByTime folder and is now back visible from the front end of the Aura.
Whilst this might be absolutely useless for most practical purposes, I was mildy surprised that it worked at all.
I'll try some other recordings, both by spoofing the file name (i.e. putting a recording on there that wasn't originated from the aura) or just as raw files and see what happens.