Executive Assistant to Select Employee in Expense Report from Employee Center Role

We have a Workflow and a deal of scripting to handle the specific requirements of the approval process for Expense Reports.  From the Workflow, the 'Employee / Entity' field is locked for edit (i.e., it's 'inline') for all Employee Center roles, except one: the executive assistant to the CEO.  This person needs to be able to enter Expense Reports for her 'Supervisor' (the CEO) as well as others on the exec. team.  Given that she is subordinate to all these staff, how can I best handle the ability for her to select an Employee whom is not her direct report?