Track Form Submissions Based Off of SEM

I am wondering if it is possible with drupal modules to be able to track whether a user who filled out a form came from an SEM campaign. For example (and I'm winging it here), if a user hits a custom SEM landing page, a cookie is set. Then when that user hits a specific form thank you page, that cookie triggers a hidden field in webform to say someone came from SEM. It doesn't have to work exactly like that, but I'm wondering if something similar is possible.