Woocommerce, free shipping when someone signs up for Mailchimp

I have found a handful of plugins that give someone a percentage discount code when a web visitor to the store signs up for the Mailchimp newsletter.

My client would like to offer a one-time free shipping code when a visitor to their store signs up for Mailchimp in a pop-up window.

Is there a way to do this?

The website is just in the discussion stage so I have no URL to share.