You might be better off just having a decent muffler shop fab a system up for you. The sedan I rented seemed to have a bit more length behind the rear axle, and I think most of them have turned down pipes, so the straight back exit might not work with your rear valance.
On top of that, an exhaust that sounds great on an ST is probably going to sound like ass on a naturally aspirated car, as they are built with the assumption that a turbo would be in the system.
I'd suggest getting a different muffler welded into your current system, or just saving up for an ST.