Unique Code to Validate Form-fill from Mailer

Hi,

We are going to be running a campaign that will have our sellers drop some swag and a card to prospects with a CTA to fill out a specific form on our website. To incentivize them, we will be giving a gift once the form is submitted. My thought is that we need a way to limit this so people cannot fill out the form with random information, fake emails, etc. to get multiple gifts. Is there a way to create a list of randomized codes that we could mail merge onto the cards in the swag drops so that when the prospect completes our form there will be a form field to enter the code and we would only let them complete the form if the code matches one that we have in some sort of repository?

Thanks in advance!

Chris