Workflow - Stop notifications and Work Items to primary user when personal substitute active.

Hi,

Can somebody please advise how to stop notifications and Work Items to primary user when personal substitute is active.

In detail,

Whenever Personal substitute is set up for user, notifications and Work Items sending to both primary user and substitute. I believe its a SAP Standard behavior. Please let me know if there is any way to handle it?

Thanks & regards,

Siva Kankanala