If you look through the Logitech Harmony Hub parent driver code, you will find the parse() routine where all of the responses from the Harmony Hub are handled. The last case that is handled is when the parse() routine doesn't know what to do with the incoming data, and thus it simply performs a log.info call to make the data available in the Live Logs.
Ok, so now all you have to do, is look at how I handled all of the known incoming messages. You can then add another IF statement to look for the incoming traffic you're interested in and then take some action. That is the harder part... What type of action do you want to take? I would recommend adding the "Pushable Button" capability to the parent driver. This would allow you to create 'button pushed' events that any other app on the hub could use.
Hopefully this gets you started... It seems like this make be a fairly custom solution, so I am not sure if I could add this to the shared code that everyone uses. Many of the Harmony remote controls do not have those device control buttons at all... We'll need to think about this for a while... Maybe some sort of drop down user preference to select the type of Harmony Remote control? But even then, I am guessing the data only is broadcast from the Harmony Hub when you've associated those buttons with an action, like changing the Hue bulb dimming level? I'd like to keep the shared driver generic. If there is a way to do that and still include support for those buttons, I am all in.