ProcessFlow Delete Workunit

I have a flow which generates a large number of activity records and is independent of a service (Standalone).  As we do with all processflow workunits, once completed we move them to history.  The problem is an out-of-memory issue that causes the custom activity moving the workunits to fail.  We made the changes to VM as indicated by an article in the knowledge base  and at first it seem to work.  My question, is there an automated way to delete/purge specific workunits so they are not moved.  I understand I could target what I want to move but that still leaves the workunits not moved as a manual delete.

Thanks