The solution is to create a QB Item (ostensibly of type Non-Inventory or even a Service) and specify the "Producer" custom field with a value of "System".

Whence the QB Item has been imported into Vinosmith you will then need to create an inventory record for that "Wine" and at this point, you can enter in an arbitrary quantity - it doesn't matter. The inventory record needs to exist because that is how Vinosmith groups line items on orders together. 

So to recap:

1. Add QB Item with a QB Preferred Vendor (Producer) field of “System”
2. Request a fetch of items so they are imported into Vinosmith
3. Create a dummy inventory record with your primary warehouse - any quantity is acceptable
4. Edit/Update the item  in Vinosmith to be "non-inventory" so it will not show up on commission reports

You can now add these “Wines” to invoices.