this will affect the P&L and is not the proper method for this situation.
@Bridge from what i have understood from your initial post, you are not selecting any inventory items on your sales invoice but entering it as a single line for the whole service by selecting a suitable account. is this correct?
you can create an inventory item for your Service (separate inventory items if you want to differentiate different services), and then make production orders including all the items you have used for the Service. you can also allocate the Service to any control account of your choice. the production order will reduce the quantity of items used in your Service.
now, you can just select the newly created inventory item Service on your sales invoice which will reduce its quantity too from your accounts.
another approach will be use of inventory kits. but this is possible only if the service consumes fixed quantity of items.
you can read the guides on production orders and inventory kits to understand better.