Cache busting for javascript widget?

We have an email subscription form in the footer of every page on our site. (The form uses the mailoptin plugin, integrated with My Emma email marketing). After submitting the form, the form is replaced with a Thank You message.

Since I’ve installed SG Optimizer, I’ve noticed that sometimes the form displays the Thank You message instead of the form, even on new sessions when the form had not been submitted. But not on every page. Some pages have the form, some pages have the Thank you message.

Is there a way to exclude particular divs or scripts from being cached? Or some cache-busting trick I can do to prevent this form from looking like it’s already been submitted?

Thanks,
Jannette