1. You want to recover the persons gamertag whos buying you the game on your xbox.
2. Then you want to download the game you want.
You can play it because it was the first xbox to be downloaded on which lets everyone on your xbox play it.
3.After the download, your friend will have to recover his gamertag.
4. After the recovery, your friend will have to download the game by going to Account Management and then Download History.
Your friend can play the game too because he is the owner but since it was downloaded on your xbox, its the original xbox.
5. You can now delete your friends profile from your xbox. Remember to chose delete profile only because then you will lose the game.
6.YOUR DONE!!