Adding additional length to an element via properties

I have a project that will require me to add length to my pipe elements such that the field can trim them to final length. Using Shape Properties: Partlist Data: Values: Addition, I can add this field trim easily & have modified my reports to add this extra length to the item in my order list. The problem I have is the weight in my report always shows the modeled weight without the extra length. This could lead to over-weight shipping loads.

Is their a way built into List & Label to add the extra length weight to the final weight? It seems I will have to write a function to break down the item to get the modeled length weight per unit then calc the new weight using the modelled length with the additional length added. If there is a simpler way please let me know...