Hi Mark,
sorry, unfortunately there's no additional (hidden) key to specify another Backup-Folder than the one in the data-folder. I'm using a small backup-tool which is copying my specified resources every day at 12:00 o'clock, including the data and backup-folder.
The automated backup from the sync and meter import should not help in case of a hard disk crash but in case of trouble with data loss during the sync - so that's just another purpose of backup.
We have built a comparable backup function like the one you are looking for but it's part of the USB-Stick Plug&Play-version only: There you can specify a folder (for each PC, the stick is plugged into) for backups and how many daily backups SiDiary will keep there...
Cheers, Alf.