As it was written before – create calendar task which will execute fallback copying every night. For such task no need to define ZWKS:MODE=FULL. MODE=DATA is ok.
So, every night during fallback configuration is saved.
E.g. you create by ZWKS:MODE=FULL at first new fallback package named MYBACKUP. Then every night this package will be updated.
Please read NED, it has excellent example how to do calendar for fallback.