Freight and additional charges at sales order header

Summary:

We have a customer with a requirement to capture a single freight charge for all the lines in the order. Meaning that an order with 10 lines, should have a single freight change of 100$.

The freight charge can change on each order, and the order entry personal manually enters the freight rate on the order after communicating with the carrier.

The freight charges should show as "shipping charges" in the sales order confirmation, and should be interfaced to AR as freight lines, not sales revenue.

When using the shipping charge list, the charges are getting applied to each order line, which is not the requirement. This customer needs to be able to manually enter the quoted freight rate on the whole sales order as single charge.