REBORN GAIDIN is right, this can be done rather easily in a one player game. To add to Reborn's solution, I used the Titans and went against the Atlanta Falcons (they are one of the worst teams in the game, and they like to pass).
I chose 7 minute quarters and using infinite rewinds is very helpful.
I had my 6 interceptions by the end of the 3rd quarter. Here's how:
Each time you're on defense, select a play By Formation, then select 3-4 formation, select Stack, and then select Cover 3 for your play.
As Reborn said, before the snap, chose X for your audible and then up on the right joystick to select man coverage.
If you want to try to intercept on your own, choose to be the Safety and hit Y for the interception when the ball is coming towards you. If you'd rather have the AI's do the work, select one of the defense lineman as your player. If the opposing team catches the ball, use your rewind as the quarterback will often (but not always) throw to the same receiver after the rewind.