Invoice UOM issue

The Invoice UOM is different than the PO UOM and is causing issues with our automated invoice processing.  We cannot use an Alternate UOM on the PO due to overflow.  Any advice on handling this on the accounts payable side,  we cannot address this on the material unit of measure side. The material
base UOM in ML. The warehouse issues to manufacturing in ML. The Vendor will only invoice in Drums or Each.  The PO is in liters, 1 Drum = 200,000.00 ML. Thanks