Cannot cancel PO because PO owner has left the organization

The following access level is defined for the standard purchase order document type: Modify

This means that everybody that has access to the PO can view, modify and freeze the document.  Only the owner can cancel the document or finally close it.

A PO has been created, approved and reserved by user/person.

Now, this user/person has left the organization and the PO has to be cancelled or finally closed in order to release the funds. Since the owner is no longer with the organization, what is the way of working to get the reserved funds for this PO released?  Using the unreserved option under tools isn't an option either.