You can pull this off in any game mode provided your opponent is labeled as a Rival (this will be indicated on the team select screen if the two opponents are rivals).
You can cheat with a buddy, or crank up the quarter length to 15 minutes and play on easier difficulty levels to increase your chances against the CPU. I'd suggest trying for this at the same time as the 6 Rush TDs with the Dolphins against the Bills or Jets, or when trying to get the 550 Pass Yards with the Titans Achievement (against Houston, Indianapolis or Jacksonville) to kill two birds with one stone.
If you have not yet won the "Score 40 points in a Rival game" Achievement, you will unlock it at the same time. You must complete the entire game - the Achievement will not unlock when your score passes 60.