How about lubricating the freehub with a slightly heavier oil? I've done this with hubs ranging from an old 5-speed freewheel to an Ultegra 9-speed freehub using 20-weight motor oil. I haven't experienced any problems in cold weather (which I sort-of expected). The hubs aren't *completely* silent when coasting but you have to listen hard to hear them. Some hubs I hear on group rides sound like loud fly-fishing reels.