Append backup to tape without autoloader

We have only single tape drive and the backup schedule is set like this :- Monday (full backup), the rest (incremental backup). We use Brightstor ArcServe 11.5 and we do not have autoloader. We intend to replace the tape every Monday and thus the backup for 1 week will be put on the same tape. May anyone advise how can we set the backup to append on the same tape ?