The file storage mechanism in Alfresco is pluggable and the use case you describe could be implemented via this mechanism. I believe the interface in question is called ContentStore but you should check the API JavaDocs to confirm.
I don't know of an implementation that does exacty what you describe, but am aware of community developed extensions that use the database, Amazon S3 and the Hadoop DFS for storing files. While none of these do what you're after a lot of the basic machinery would be the same.
Cheers,
Peter