I'd suggest using a T-SQL script to restore from. Whatever mechanism is changing the backups nightly is surely discernable, and therefore repeatable. You can then just run the restore. There is no RESTORE FROM Database command. You must have a backup. If you have to, you could take a backup of your own, but then, in case you have differentials, make sure you use COPY_ONLY for that backup so that it doesn't disrupt the differentials.