Not over XBL. Maybe over a system link. You can have Guests on the same box.
Connect you controller, then go to the Campaign or Multiplayer lobbies. You should see a "Hit (A) to Join" under your signed in account. Hit A, then you'll be prompted to sign in with a gamer profile. Hit A to say Yes. Hit A again when the Guide screen comes up. Hit down once on the left thumb stick to select "Guest: Xbox Live". Hit A twice and you should be good to go.
To log out from a Lobby, hit the guide button. Hit the X button to "Switch Profile". Hit your L thumbstick up to select "Yes, sign out." Hit A. Hit B to go back to the screen, then hold down the guide button until a prompt appears from the right of the screen. Hit your Left Thumbstick up once to select "Turn Off Controller" then hit A.