Whenever an invoice is created from a salesorder is created, the order number on the invoice is automatically populated  with the salesorder number.

It would be great if we had better control over where the order number for the invoice is coming from. In our case we have a reference number on the sales order which would like to use instead.

Currently:

SalesOrder.Sales Order# =>  Invoice.Order Number

Desired Outcome:

SalesOrder.Reference# =>  Invoice.Order Number

Is there any way to customize where the Invoice Order Number is coming from?