Ok, so this is an interesting question.
If there are Hydraulics on your mill, you could tap 2 lines and use remote cylinders to solve the 2 most pressing problems - moving the saw to line up the trim cut, and setting the height/cut depth for the saw (and a limiting switch that so as not to run the trim saw into the bed :-).
Tapping a 3rd line run to a hydraulic motor, with another slave cylinder control to run a small circular blade mounted on a movable set of rails. A sealed bearing, on a 1/4" angle could hold the vertical cylinder, which could parallel a vertical track for the motor head to ride on.
To move in and out of position the hydraulics extend the saw on the rail that moves parallel to the main blade, and runs in front of it. Use a Horizontal mount hyd. cylinder mounted to the main saw frame to move that left to right, Use another with a long throw (20" or more) to raise and lower on a vertical bar mount.
That;s a lot of expensive hydraulics though. Motor plus 2 pistons, Slave cylinders, remote controls, taps, 200' of hydraulic lines, fluids...Thousands! Plus labor.
And you have to keep that saw sharp too.
I wonder if Cooks Saw has the parts?
:-D