I'd hook in where the heater lines come off to go to the cab. Essentially, I'd install the filter inline with that heater hose, then put a T that would cross to the return, and put a shut off valve in between, then T into the return. In the winter you'd close the shut off to make the coolant go to the cab, and in the summer you'd open the valve to let the coolant by-pass through the Ts instead of baking you out of the cab.

I've considered doing this, just needed to find a filter base, but never looked. Let us know what you end up using. I was thinking of using the ones for the C series Cummins engine, as I already use them on my combine.