I haven't seen anything to indicate an ST swap with an auto in a sedan has been done before. There have been at least a few ST swapped sedans, but the whole drivetrain. I am unsure if any of the factory autos offered in the Fiesta would bolt up to the 1.6 or not.
I believe there was a FWD only escape with the 1.6 ecoboost and an auto transmission in the past, so the ECU/TCU combo likely exists, but it is unknown if that transmission will fit in the Fiesta chassis. Even if it would fit, I have my doubts that it would be a simple swap with the chassis and suspension differences between the two. (maybe even an auto 1.6 Fusion?)
If you are looking for more of an ST like experience, components like suspension, brakes, chassis bracing, wheels, etc. are essentially bolt-on (whether factory or aftermarket).
Ultimately, and ST sedan swap is a major undertaking, even with the full drive train which is bolt-on-ish if you have a donor car with the mechanical parts and electronics.
Given enough time and money anything is possible, but its up to you to decide if its worth it.