That's very much like what I do with Gravity Forms and the Display Posts plugin (not sure if you have either). It's documented here for what it's worth. If you have Gravity Forms it'd allow you to guide the creation and auto create the shortcode for whatever widget. I've also built cut/paste HTML generators in Google Spreadsheets to help guide people towards making stuff like this when I didn't have Gravity Forms. They'd fill in a few cells in the SS then cut and paste from the big green one into their post. Not pretty certainly but it works.