It is possible to archive the config via TFTP, but this is not recommended for security reasons.  For one, files on a TFTP server must be universally readable and writeable.  If others have access to this server, your device configs can be compromised.

The second problem is that most TFTP servers require the file to exist before they can be uploaded.  This presents a problem with each config revision will have a unique name.  However, if you pre-create all possible file revisions on the TFTP server, then it should be possible to archive to that server.

It would be better to use SCP or at the very least, RCP or FTP.