How to default max of actual_ship_dates to the GL_Date of a non-shippable line in the sales order ?

We have enabled GL_Date to have System Date for the non-shippable line using service mapper. But that is not solving the purpose of having 'one invoice for one sales order'. Our concern is that if the system date changes to the next day for any reason, the non-shippable items will get the system date as GL date while the shippable items keep the actual ship date. This can result in two separate AR invoices being created.