Inventory Management

We just started using the Quickbooks Online inventory management part of the package.  We're a home remodeling company doing whole house, kitchen and bath remodels along with repairs and other home improvement work.  We keep an inventory of basic plumbing and electrical supplies in our small warehouse.  Things like plumbing pipe and fittings, electrical wire, boxes and devices.  We entered all of these items into QB online.

When we do a quote for a job we create an invoice to "remodel a bathroom" that would include all the materials we need to do the remodel job.  But because we don't know exactly what supplies will be needed they aren't itemized on the invoice but are included in the cost.   As we pull things out of inventory we want to subtract them from inventory and get an understanding of what the job cost us in supplies to make sure we're bidding jobs profitably. We do not want to invoice the customer for the parts we're pulling out of inventory.

We mistakenly thought we could use "expense" to do this, however when you put something on an expense it actually adds to the inventory, rather than subtracting it.  QB help advised that we should do an invoice and mark it as paid.  This will cause issues as it would show additional income when there isn't any.  I really don't want to zero out the cost in the inventory because that will make it difficult to track the expenses.

Is there a way to do this without going to a third party inventory management program outside of QB?