Leonardo Serial Query

I am totally new to Arduino, so I am very hazy on the terminology…
I have a project I plan to complete, which controls the switching of a number of relays, using an established protocol (called OTRSP - Open Two Radio Switching Protocol).
The project that I saw published used a Freeduino. I have purchased a Leonardo, with a matching protoshield. I have not commenced building the project yet, as I wanted to clear up this point first:
The OTRSP protocol uses the DSR signal on the serial comms to determine which of a particular pair of outputs is active.
On the Freeduino, there is a separate RTL232 chip and the original author jumpered the DSR output of the RTL232 to the PD2 pin on the processor, via a 1k resistor.
I note there is no separate USB-RS232 converter chip on the Leonardo. Is it still possible, using software, to access the DSR pin and use it to set the appropriate output? If so, what changes would I need to make to the sketch to suit the change in Arduino type?
Or have I bought the wrong type of Arduino for my project? :~

I would be grateful for some advice.