Thanks for checking back in with us on this. While the ability to add existing listings to consignment items is still on our list of potential enhancements to consider when planning future site updates, we still do not have any definitive plans to add this option to our suite of consignment tools.
Therefore, the only way to associate listings with consignment items is to post them through Auctiva and link them with the desired consignment items during the listing process. As it stands now, I expect it to remain this way for the foreseeable future.
I'm sorry that I cannot offer you more encouraging news, but we appreciate you posting here to let us know this is something that you are interested in being able to do.