UC CCK Pane does something similar and gave me an idea...could someone come up with similar functionality as an extension of node_checkout, which is more feature-rich and more widely used than the uc_cck_pane, where instead of directing the user to the node/add form integrate this into a checkout pane so that it's part of that process. This would significantly improve the workflow of uc_node_checkout to remove the extra step of node creation...just an idea. :)