Rewarding Facebook requests

Hi Guys,

As far as i know, developers are not allowed to reward people for simply inviting Facebook friends to our games. That's why I'd like to reward players for every accepted request (every invited user that has installed the game). The only solution that comes to my mind, is to store all the requests on a server, and then, when a user logs into the game, reward players who have invited him. But that unfortunately requires a server... Do You Guys know any solution that uses only the Facebook API? I'm developing for Android.

Best regards!