I wouldn't think it would be too difficult.
Hose from head goes into aux coolant pump then into servo thingy.
than into the firewall.
So just bypass the servo thingy put in a valve so you can shut it off.
It shouldn't matter which way it enters and exits the firewall It's just a heat exchanger right?..There may be a swizzle where the aux coolant pump
is controlled by the servo somehow..not sure..you should research that .
But if that was the case a simple switch inside the cabin somewhere can turn the pump on and off.