Sending a list of missing items through a workflow?

When a new project is received, we enter the information into our Smartsheet, through a form, including checking boxes of the required elements that were submitted. I have a workflow set up to notify a client (non-Smartsheet user) that they are missing an item required for their project review. It sends them an email to update the form by sending an attachment. Right now, it pulls the list of items already submitted.

Is there a way to alert them of the items that were NOT submitted from this list?