Ahh, I misunderstood the question.

It is possible that you gave Google permission when you signed up.

I think it is more likely that the URL has all of the information Gilt needs to process the request:

    http://www.gilt.com/google-
    chromebook?opromo=Google_Chromebook&ocl=Email&ocat=Link&
    email_address=<any email would work here>

I visited that URL and replaced the original e-mail address with a different one and it worked fine.