Ok, there are two ways we could do this.
1. you give the plugin the ID of a form, and before it prints it loops through the form and checks if each input field has a value. This seems, buggy at best.
2. you already have, or write some kind of verification function that checks the form for valid entries, much like the function that is run before form submission. We would add a pre-print callback field where you could enter the name of this function. This would be more advanced, but way more flexible and stable.
What are your thoughts on this?