Well it turns out that the HP un2420 cellular modem has an inbuilt GPS that can be turned on and off.. So a bit more google foo and I found all that was necessary is to echo a command into the third enumerated serial port like so;
#$ echo "\$GPS_START" > /dev/ttyUSB2
Then we can just point our favorite GPS monitor program at /dev/ttyUSB2 and we should see NMEA data. I used gpsmon to test mine. I was amazed to watch this working on my bench inside the shack.
Now my Wenet ground station can easily go portable with Cellular data and GPS position information and no USB 3G dongles required.