Just curious how many line items there might be. Hundreds? Less than 100?
I’m still not sure I understand the intended UX, but if you need to iterate over a RG, I assume you’re aware of @vini_brito’s Orchestra plugin (original announcement here).
I’ve not used it, but I believe it would allow you to run a workflow for each cell (and thus access/save each line item’s input values, etc.) Of course, there’d be an http request for each line item, but if that became an issue, you could probably get around it by using auto-bind and scheduling an API workflow on a list.