Pre-fill embedded form with email address
We are hosting embedded Marketo forms on our website. When a user fills it in, a thank you page loads. If the user did not opt-in on the prior page's form, a query string vaue "opt-in" is updated to "no," which triggers a dynamic section of the web page to display soliciting the opt in. This section includes a single field form to capture email address and opt the user in.
Because the user would have just filled out a form on the previous page, we'd like to populate the field with the email that had just been submitted. Originally, we were passing the email value in the query string, however that went against GA compliance since we would have been capturing PII in our web analytics.
Is there another way to leverage the Custom HTML for Known Visitor or other Marketo-based capability to enable this functionality?