Multiple DAT Drive Backup

We have just toppled the the 4Gbyte capacity of our HP9000 DDS2 Dat drive during our informix Level 0 backup. (ontape -s -L 0). Subsequently the ontapecommand prompts for a second tape some 40 minutes into the backup procedure. We have a secondary DAT device attached to our HP9000 server which is currently unused. Is there a possibility of utilising both DAT drives to complete the backup process without the requirement of user-intervention to swap the tapes. Another approach we have thought of is to enable compression on our primary DAT drive thereby giving us a maximum 8Gbyte capacity. The issue here is that there is no guaranteed compression ratio and therefore the tape capacity is variable. How would this be specified in the tape parameters? Any help here would be greatly appreciated. Paul.