I'd quite like to see it in the C-Store too. I've actually 'referred' three people to the game, but for two of them I didn't know about the RAF system and the third didn't use the code properly or something.
I would say DON'T add this to the store. Its too easy to acquire. Getting one person is all you need, or buying another copy of the game and a game card. I have never said this, but, not everything needs to be in the cstore.