A radiator muff helps a LOT but you can always try a different heat exchanger.
Can even use the choke puller and cable for this if need be. My choke system is not being used at all but the puller and cable are there. Wonder who else has theirs in and not using it.Personally, I would construct a fresh air flap. Connect it to the fan speed cable so that you can open and close it. That solves the winter issue. I have no idea why they don't do this with the original design.