How to install Zigbee2MQTT for 'non-standard' Zigbee adapters

I’m using an Ethernet attached Ember Coordinator.

Service description for the Ember gateway:

[Unit]
Description=socat-for-zigbee
After=network.target
[Service]
ExecStart=socat -dd pty,link=/dev/ttyzbbridge,raw,user-late=openhab,group-late=dialout tcp:192.168.1.170:8888
Restart=always
RestartSec=30
[Install]
WantedBy=multi-user.target

Now trying to install Zigbee2MQTT via openhabian-config.

Problem:
openHABian doesn’t offer /dev/ttyzbbridge as an option and doesn’t offer the possibility to enter a user defined device path:

The device offered is a Z-Wave stick.

Question:
How do I install Zigbee2MQTT on openHABian for /dev/ttyzbbridge?