SmartJobBoard modification - Recruiter tracking addon

My business pays recruiters for sending new people to register at my website.

I need a modification that will record the recruiter's referral code into the new user's profile when they sign up.

The link would be like: http://www.myjobs.com/job.php?post=3&referral=12345

So a recruiter should be able to login and 'Email a Friend' a link to the job that automatically includes his referral tracking code for us to give him credit for the new applicant.

The recruiter should also have this link to copy & paste into an email that they would use in mass mailings using their own email client.

The link would go to the homepage or a specific job post. When the new applicant decides to register at our site, then the recruiter's referral code should be pre-filled or hidden, but stored in the database when they complete registration.

So if they click a recruiter's link, and browse other pages on the site, the recruiter's code should stay with them and be submitted if they choose to register. Using a cookie maybe? Or a [SESSION] variable?