Is it possible to setup an employee center user to approve POs if they are not tagged as a purchase approver or supervisor of an employee?

On the custom workflow, you can set the condition to expose the accept / reject button for that specific person instead of the next approver.

THanks Mika - yes but i dont thin kthey can even view a PO if they arent a supervisor/expense approver- no?

Right, so is your original question whether an employee centre can approve POs? I believe the answer is no, actually. I believe they can approve vendor bills, but not POs.