I want to manage some material stock in my inventory which will be consumed when an order is confirmed. It does not quite work for us to add this to a product's BOM, as the amount of material used can change from order to order and is decided by the person that writes the quotations.

So I thought how about having some product that has it's stock managed and that I can add to a quotation and/or invoice, but that does not show up on either of those documents as presented to the customer.

I could also add this material to the list of upselling products so that when the main item is added, the user is reminded to also add the hidden entry.

Is this at all possible? If so, how?