This wouldn't be the most aesthetically pleasing alternative, but I wonder if you could just slide a 3 foot long piece of 8 inch PVC pipe over the treated 4X6 and fill the top 8 or 10 inches of the space between the PVC pipe and the wooden pier with vegetable oil???? Since the oil floats it will stay confined inside the pipe and allow the pipe to slide up and down along the pier as the ice layer rises and falls.
I guess if you wanted to, you could fashion some sort of a wooden facia on the outside of the PVC pipe with some 1 inch plank lumber to hide the pipe.
