Order import to use Reference Key ID to avoid Duplicates

We use another system that assigns a unique Reference Key ID number (they call it External Ref ID) to the orders to prevent duplicate entries when creating new records.

If by mistake we upload the same file twice to Americommerce, the orders get duplicated.

We need to leave the Order ID blank so Americommerce knows it's a new order, but if we could specify a Reference Key ID for each order then the system could prevent duplicate orders if the Reference Key already exists.