I learned that it is indeed possible to do as I hoped.
The Freezer's flapper valve that shunts cold to the fridge to do the job ov cooling is the thing that must be controlled.
So it's a question of altering something about solenoid
Either build a little circuit that reduces voltages sufficiently to power the solenoid which is might (or not) be drawing A full 120 VAC. A multi meter on the power leads to the solenoid will answer that forthwith
Worst case is that the fan and valve require a lower voltage in DC, which can be supplied VIA any respectively sized Power Supply and old Computer PS units supplies provide a variety of very smooth DC power through the various leads which you can even combine to get higher power increments.
Then re route the power to the solenoid to a power supply which is controlled by the Johnson Controls unit. And Presto-Chango you will have the solution.
I gotta say it's a much more elegant solution than interrupting the power to the whole fridge and wiping out the freezer function.
However:
I own a couple of window Air conditioner units that I don't use since the HVAC install I did and it occurred to me that the more elegant solution is to build a cold room from ply, sandwiched around center ripped 2x4s and insulation. I even have 6 foot thermal pane glass that will make up some really slick doors. I can drive the cold room with an AC unit by by passing the thermal switch and using a Johnson Controls unit to regulate the temp.
Hell I can even create a multiple cold zone cold room with one for Lagering and one for Ales by installing a partition with a valved duct and a fan slaved to another temp; control. The down side Is I'll be warming the Cellar with the exhaust heat from the cold but, so what? I mean what do I care if the Cellar is a touch warmer?
And on the up side ( again) a cold room can be customized to accommodate pretty much whatever application I want. So If do decide to buy or build that conical fermenter I can make it large enough so that it'll fit. You won't get your conical 20 or 15 gallon fermenter in a fridge.
So I'll be buying some lumber and insulation instead of a fridge.