Only add contact form submission emails to MailChimp that opt in?

Hi all! Is it possible to automate adding emails from form submissions to MailChimp only when the person opts in through a checkbox field I added asking if they want to be added?

Please see this contact form example: https://lindsaymcgowen.com/contact

I added the opt in question to the very end of the form.

I've been scratching my head about this for a while so any insight would be very appreciated!

This is what I want to do too. Did you ever get an answer?