How do I add items to an invoice that has already totalled my shipping costs?

[mrshickadance]

I requested for an invoice to total my shipping costs from a seller, but then I saw something else I wanted to add to it but ebay will not let me add any news items to the invoice. The seller is willing to let me add those items to the invoice, but thought that there was an option somewhere in the cart or on the invoice, which I could not find. Is there any way that I can add items to an invoice that has already totalled the shipping costs?

[nubian_treasures]

The seller would have to list the other item as a buy it now for an agreed upon price and let you know when it has been listed. They could list it as "for mrshickadance only" and not show pictures. You would buy it and then it would show up on the combined invoice. If after you get your items and you and the seller are satisfied with the transaction,