The way the tackle calculation works, in theory, is that the sim first determines if the defensive player is in reach of the target. If they are, they make a tackle attempt. The QB, has a number of tools that are consulted to help determine the success or failure of the defenders tackle roll.
So, the Sim already goes through a progression of abilities, Does the QB have Turn the Shoulder? Does he have X, Does he have y, and it goes through the progressiosn to see if he can avoid the tackle.
So, running or passing it doesn't MATTER. You just add the 'Pump Fake' to the very bottom of the checked attributes and if it is available, the QB can use it to attempt to avoid the tackle by freezing the defender with a pump fake.
Problem at that point is making it 'fair' and increasing the fumble percentage for the QB who goes through their tackle avoidance progressions and gets down to 'Pump Fake'.