Currently, the associations with creator are on an order item alone. It would stand to reason to make that association with the purchase order rather than the line items (or various people add orderitems to a purchaseorder?)
Whatever the solution, it would be useful to associate your purchase order with something other than the orderitem so you can retrieve it from your page.
A small sidenote: best practice for data source microflows would be to give them the DS_ prefix rather than an ACT_ prefix.