Default Unit of Measure for non-stock items when ordering direct from vendor

We are testing ePro Requisitions 9.1, with multiple hospitals and physician offices using one item master for the entire company.   We are having some issues with unit of measures defaulting appropriately on non-stock items that we are trying to figure a way around so that when the item in the item master is ordered directly from the vendor not sourced to inventory that it defaults properly for that POBU.  Anyone deal with anything like this?  Thanks in advance for any insight you can provide.