Thanks. I'm going to try that on the next pair. My floats look nice and loose (i.e., they actually float) already, but it won't hurt to try it inside out. For socks, I think what might do the trick (if that doesn't), and which I've heard another sock knitter recommend, is to increase about 10 sts along the way to the ankle hinge, then decrease once you don't need them any more.
As for which fibers to use for Fair Isle socks, I would steer clear of 100% cotton, linen, or silk, because they don't stretch. And I probably wouldn't use alpaca unless you're going for extremely warm socks. So far, I've just used 100% wool and then added woolly nylon in the toe and heel to reinforce the areas I tend to wear out.