Try the python code in the GitHub repository linked in this article. Save switch.py and switchstatus.py from GitHub to your home directory.

https://github.com/whit98c/Experiments/blob/master/switchstatus.py
https://github.com/whit98c/Experiments/blob/master/switch.py

The code is based on this original article
http://www.roman10.net/2011/06/23/serial-port-communication-in-python/#comment-1877

Here is some more info about the commands in case you need to use output A as well (for my purposes I only needed B). These are also listed in the wiring diagram.

http://support.monoprice.com/link/portal/41053/41056/Article/92/What-are-the-Hex-codes-for-the-4x2-True-Matrix-HDMI-Switch-w-Remote-PID-5312

On an Android device, install the SSH Button app. Configure it to run "sudo python ~/switch.py X" where X is the input you want to use.