What's your goal? A "control pad" with buttons like home, jog, etc?
Probably the best way to do that is, as mentioned above, a button pad to an arduino (or ESP8266 or ESP32; they've actually become cheaper than arduino boards, and the ESP32 has the advantage of having two UARTs) and connecting to the same port where a PanelDUE connects.
Then a very simple sketch that say "Button x pressed, send G28", button "jog up pressed, send G91 G1 Y100 G90", etc, etc.
If you DON'T have a PanelDue that's really it... if you DO, then two uarts and "pass through" would be the best approach. Just a tiny bit more code in the sketch.