The STA's exhaust system is no different than any other model of ST, except for the tail pipe that runs out the rear with the SS tip, rather than the side exit on the XLT/Limited. Otherwise, same OEM muffler and resonator.
It would be cheaper to have a custom single-out exhaust run the way you want it with your preferred tip and muffler.
I don't believe that there's room for a dual-style exhaust on the Gen 2 ST.