Add a Leadpages integration and point Leadpages' form-submitted webhook at it. Each submission becomes a lead from the form's email, phone and name fields, tagged @leadpages/<page path> (for example @leadpages/webinar), so you can filter reports and build funnels per opt-in page.
Paste the BrainyMetrics snippet into each page's head tracking code too. tracko.js then usually identifies the visitor from the form itself, the webhook confirms it, and the lead keeps the ad they came from.