Roommate Code - Event Registration Form

Hello, 

I am creating an event registration form for a 3 day event. It's simple form, name, address, purchase ticket. The only complication I am running into is roommates. Here is the setup I would like to do.

1. User fills out the form, registers and pays for event. 

2. User receives confirmation along with a digital code (this code should be generated each time uniquely)

3. User shares their digital code with their roommate

4. Roommate registers for event and is prompted to enter the digital code. 

The code offers no discounts or anything like, it's just a means of automating and matching people who want to be roommates.

Thoughts?