Widget Blocks Plugin

I use this plugin and would like to add an empty field for a subscriber’s email address and link it to my MailChimp list. I have a widget block set up for an ebook I’m giving away and would like the reader to simply fill in an email address and click on submit, thereby adding that email address to my mailing list on Mail Chimp. Is it possible to add an empty field for that mailing address and how would I do it? Thanks!