Updating "Last Email" and "Last Call" fields in the Accounts and Contacts Modules

In my Accounts and Contacts Module I created fields named: "Last Email to (Account or Contact)" and Last Call With (Account or Contact)".  The fields are set with calculated formulas that read: maxRelatedDate($archived_emails,"date_sent") -and- maxRelatedDate($calls,"date_entered").

The field is updated any time the Account or Contact Record is saved.

I've recently discovered that scheduled reports that "encourage" sales folks to keep in contact with Accounts and Contacts are not accurate because logging a call or sending an email doesn't trigger the field update.

I'm trying to find a way to trigger a no-op update of the Contact and Account records so the field gets updated when a call is logged or email archived and the reports will therefore be accurate.

Any ideas?

P.S. (We don't have any custom code in our installation - everything is done with Studio and BPM).  Thanks.