Prefs BACKUP to previously remembered path

To automate the backup process from the jscript button the following command may be used: Prefs BACKUP=all TO /desktop/PrefsBackup

However, if I don't specify the TO parameter, the backup process will not be automatic/unattended (a Backup/Restore dialog awaiting user interaction will pop up). I'd like the backup to be automatically done to the user-preferred path (i.e., the one that is already remembered in the "Backup/Restore" dialog when started manually). Is that achievable?

For example along with TO parameter something like TO_DEFAULT could be introduced?

You could make the script ask for a path and then store it in a persisted variable, which it checks next time to avoid asking.