"Play Games" special promotions

I thought up a pretty cool idea that I don't know if you guys planning the Play Games section have thought up. Would it be possible to set up a "special promotion" system, where people will be able to purchase our game at a discounted rate by providing a unique code? For example, let's say we have 20 beta testers that we'd like to thank by giving them a copy of the game for $5 or so, as opposed to our chosen price of $20. Then 20 unique codes are generated and distributed to the team members. I say 20 different codes because if we generated 1 code, that doesn't stop the people from distributing the code and allowing other people to get a discounted copy. I'm sure someone could give their unique code to a friend, but since the code can only be used once, only their friend would be able to use it. What do you think? And how is the Play Games work coming along?