I'm sure this doesn't count, but back in high school my brother and I decided to a sim-only franchise in Madden. We each took control of a team, did all the FA signing, drafting, preseason training drills, and set the depth charts. The only games we would play are the ones where we played each other. We simmed everything else. It was a blast.
Pro tip: In Madden 2004, O-line is by far the most important position in the game. ;-)