Order rules: option to add weight to an order to cover shipping boxes/void fill

We consistently get penalised by our couriers for under declaring our weights, this is because mintsoft uses the sum of the product weights as the declaration, but the actual weight of a parcel is the sum of the weight of the products and the outer packaging and void fill used to ship it. There is an order rule to change the weight of an order but not to add weight to an order. I am would welcome a change to the order rules to introduce the ability to add weight to an order so that the weight of shipping boxes can be added to the order and make the declaration accurate.