Forms 2.0 Success Message on Embedded Form

Looking for help on how to add an OnSuccess message after a Marketo form submit on our website. We want to avoid a Marketo 'Thank You' LP so it doesn't break the session in GA.

The form submit results in a page reload and brings the user back to a new, blank form after submit in its current state... We want the submit button to trigger a Thank You message underneath so we can set up an element visibility trigger in GTM. What would the form's embedded code look like for this?

Any help is appreciated! Sanford Whiteman