Add variable to disable new disk destinations

In http://drupal.org/node/373790 a solution was implemented to block backing up to files (to force users to download their backups instead). This was done through a variable in settings.php (backup_migrate_allow_backup_to_file) that disabled the creation of new disk destinations, and also deleted the default ones.

I was wondering if there is any interest in a similar variable that only disables creating new disk destinations but leaves the default ones in place. If there is, I could work on a patch.

Thanks for a great, and very useful module!