How to delete the archived messages?

Archiving is setup and running in our PI systems. ( I used the SDN doc, "Archive and Delete Messages in SAP. XI: A Step-by-Step Guide")

I'm now looking to automate the deletion of the archived messages (NOT the deletion of the original message in the DB, but the data that has been written out to the O/S -- the actual archived data file.

Any pointers on how to accomplish this?

Thanks in advance.

-Joe Rufo