can’t withold sniffing 
there, already 
There is this thread referring to some PGN that might receive nudging from some button:
When I’m not mistaken, this is the (current?) definition of this PGN
‘Boards/PGN.md at main · AgOpenGPS-Official/Boards · GitHub’
So, in standard setup,
- AgOpenGPS on the WIN tablet sends some PGN via UDP to the teensy, to tell about desired steering angle
- some other box may send other PGN via UDP to (where? - the teensy? the main application) to request some nudging
My idea now is to have two distinct installations of AgOpenGPS, one on the seeder and one on the tractor.
And some “man-in-the-middle-tweaker”, capable of receiving, parsing, sending PGN.
As linux-addict, I think of some perl script, maybe with the help of netcat or so.
This middle-box acts as steering for the seeder, i.e. it receives desired correction of the track.
And it acts as "nudge-button-set" to the tractor, i.e. it tells it to perform that correction.
May be, some PID loop may suffice for first trials.
Even the sidehill correction might easily be added at that point.
It’s just required to hook into the PGN-over-UDP link.
As Wikipedia tells us, PID has been developed by observing the actions of helmsmen on ships in narrow tracks. Not that different from keeping a seeder on track? And I even think that my own manual steering resembles some concepts of PID.
Early testing might be possible with lightbars, too.
The goold old track markers are just one SCV button away for assistance.