Assign Contact to a Promo Code

I am new to Eloqua 10 and I am trying to solve the following:

I have a campaign where selected customer get an e-mail with a promotion from a third party vendor. They have to fill out a form, and then they are redirected to a landing page where they are given their promo code.

I have a list of 100 Promo Codes given by the vendor, and I am targeting to 200 clients. The promo codes are housed as a custom object, that is not mapped until the client submits the form.

As of now the custom object only has two fields, Email (to map to contact) and promo code.

What are my options in E10 to map a contact to a promo code, only if they submit the form?