Form: Display Missing Required Fields on Custom Error Page

Hello;

I'm working on a site where the webhost uses NMS FormMail.

There are several 'required' fields on my form and as such, I have set the missing_fields_redirect option to send users to a custom error page if these fields are not filled out. When I reach the error page, I see the missing fields are displayed in the address bar of the browser. However, I would like to display these missing required fields on the custom error page. Does anyone know how to do this?

Thanks!
2nJenn