If you know termination impedance of 3rd port , write a matlab script.It's very easy to implement complex matrix reduction . You can find the formulas for 3-port s-parameters to 2-port..
We can use 50ohm terminaton of 3rd port. Actually I no need this 3rd port besause it's isolated port(switch), so we have 2 port system in this case.
I'm very bad with matlab, several years ago I'm work only with signal processing(FFT).
Please post here what you think that I need for this script, will be usefull if I don't find ready program. Also any similar example if you have.