It's quite easy. All you have to do is:
1. Recover your friends gamertag onto your console.
2. Sign in on your friends gamertag.
3. Go to xbox.com and sign in on that also (as your friends gamertag).
4. Hover over the support tab and click license transfer.
5. Follow the steps.
6. Once licenses are transfered go under account management on your xbox 360 (while your friends account is stil signed in).
7. Go to download history and hit the download again button.
Thats it!
ALSO..YOU CAN ONLY DOWNLOAD FROM A PERSON ONCE PER YEAR.
Feel free to add me: SaMe oLd JT