If you're looking for something like a shoe cover then I'd suggest a shoe cover!
There are nine kinds available at Performance http://www.performancebike.com/shop/...tegory_id=1344. I think I have the Descente Element shoe covers, the 3mm neoprene is wind- and waterproof but more stretchy than the heavy neoprene of some others like the Performace bootie. Also, the zippers on some (like the Performance) don't lock well and come unzipped. They all have openings for SPD cleats, these work fine with my Sidi mountain biking shoes.