Add another calculation to SubTotal
It's probably a simple thing that I'm just missing, but I've setup some special product attributes, that I don't want included in the Item's 'TotalPrice'. So I've made a calculation called 'AccessoryTotal' which adds up all of the accessories that have been chosen for that item, but 'AccessoryTotal' is not added to the 'SubTotal'. What is the best way to have 'AccessoryTotal' included in the 'SubTotal'?