How do I sign into EA on Xbox 360? How to connect EA account to Xbox Live Acct?

How on earth do I sign into EA on Mass Effect 2 on an Xbox 360? I've spent HOURS trying to connect my gamertag with my EA account with no luck. I mean there is no option for me to sign into EA when I start up the game. Only the very first time I started the game did a pop-up screen appear saying that I should sign in to my EA account but it never actually gave me the option to input my EA account details... What gives?

I'm only doing all of this because I want to play Mass Effect 2 without internet connection and it seems as though if you have any DLC's you have to be signed into Xbox Live in order to load a saved game (if you are currently doing a DLC). 

I heard that if your EA account and Xbox live account are connected, you can play the DLC's without internet connection, not sure if this is true or not.