Is git-annex still alive? Last time I tried to use it, it was very rough, and the official wiki (that serves as doc + bug tracker) gives database errors trying to create an account.
Details: I wanted to have a remote I can push to but anonymous users can only pull from, couldn't piece it together.
* Initial setup includes git filter rules so that "git add" automatically uses get-fat for matching files (no need to remember to invoke git-fat when adding/changing files).
* It works by rsync'ing to/from the remote. The setup for this is in a single ".gitfat" file, separate from the filter rules.
* You do need to run "git fat push" and "git fat pull"; this can probably be automated with hooks.
So just offhand without even trying to think about the "right" way to do what you want, the committed ".gitfat" could be to a read-only remote, then you can swap it with your own un-committed file for a push that has an rsync-writeable remote.
Also, the whole thing is a single 628-line python file, so worst case it would be easy to tweak it to read something like ".gitfat-push" and not have to manually swap it.
Details: I wanted to have a remote I can push to but anonymous users can only pull from, couldn't piece it together.