Creating the dummy profile is pretty easy man. Go to your Xbox dashboard and sign out of your original profile. Then just create a second profile. Next, I dont know if everyone else went through these steps, but what I did was launch Madden with the new profile. I configurated all my settings on the new profile exactly like my original profile settings.
Afterwards, I just loaded up my original profile and jumped back into my franchise. Once you start your franchise, just select the cpu team with your second controller and your dummy profile will be the default for the second player (if its not, just select it). Start up your game and change sliders to your liking with the second profile, then move the controller select back to cpu and play as you normally would. The cpu will then use the sliders that you chose on the second profile. Thats it.