Found this on gtuts just posted. Idk if it works but u could try.

1.) Sign in the higher level account on PLAYER 2 and click on Xbox Live to enter the lobby then hit B.

2.) With PLAYER 1, go down to options on the multiplayer menu and hit A.

3.) Press B on PLAYER 2 and sign in the lower level account and press A on PLAYER 1 and sign into the higher level account and hit Start.

4.) Now you sign out of PLAYER 1 and with PLAYER 2, click Xbox Live then sign back into both accounts with PLAYER 1 on the second control and PLAYER 2 on the first control.

5.) Go to Lobby leader boards and scroll to the higher level accounts stats (have to have account added for this to work) on the second controller.

6.) Have a friend invite the second controller then it should of worked.

Hope this helped. Also this may need a few attempts to get it right.