For UPS WorldShip where do I grab the ShipMethod for a sales order?

Does anyone have a recommendation of where I can tell UPS to pull the ship method for a sales order?

UPS wanted to use the tsoSalesOrder.DfltShipMethKey, but we noticed that wasn't the correct ShipMethod imported from EDI. Once a shipment was generated there is a ShipMethKey in tsoShipment that was the accurate ship method. I can't use the table tsoShipment to get the ship method because we batch commit and no tsoShipment table exists at time of UPS scanning an order.  I contacted sage and they couldn't help me figure out where this ShipMethKey is coming from. Any ideas?