"Consumables" billing type in Manage Charges and Estimates

Summary: I have defined a SAC called Consumable and tied it to the right order type/line type. I have attached the right Billing type as well. Now, how can I add the Consumables I use up in the field service Work order -> Manage Charges and estimates UI?

Content (required):

In Manage Charges and Estimates UI (accessed via Work Order -> Charges button) there are 4 tabs -- Parts, Charges, Labor and Expenses. But there is nothing for Consumables. I have a scenario where the Coverage in the Subscription attached to the Asset (which is on the WO/Charges header) gives a 100% discount on Spare parts and labor, but the consumables will get a 10% discount. So I need to be able to add Consumables.