How can I add custom freight charges post-purchase on orders?

[Bushycreative]

I have a use case where the customer will place an order and then the fulfilment will add calculate the freight afterwards to charge the customer. 

Essentially the customer would place an order, the fulfilment will approve it and add the freight amount and then charge the customer (or request payment).

I know this is clunky but it's a b2b system for franchisees to order merchandise so it's a bit different. 

Any ideas?

*I originally thought I'd just have it so they 'edit order' and add a shipping rate but found out you cant edit shipping in the order, then i thought we'd have an item named 'freight', but realised you cant set a custom price when adding a product to the cart?

[dakshyafreond]

May be initially create Draft order and add charges by Freight. Then send full order for payment.