Ask HN: What's the easiest way to add invite codes

I'm at the point on a project where I want to add invite codes and share it with a select few people (and slowly grow it after that). I'd prefer to not to add another table and a bunch of logic to the core app itself, knowing that I'll just tear it out in a month.

Anyone know a good service for this? Any other good methods?

LaunchRock: if you're reading this, this would be an awesome addition to your service.