I'll have to think how to do that - my GPS is kinda buried in the car now...and I don't have ethernet there.

It's an Oncore running in NMEA mode, Software command set available here. (Warning 2.5M pdf). The NMEA command set starts at page 142.

I don't know if the software I used to configure NMEA mode turned on GPVTG or not, which is what gpsapp appears to be using (from a quick glance at the source anyway). Does gpsapp deal with this, or doe it expect to find the messages already being spat out?