Fortunately, this is pretty easy. If I finish a bottle while cooking, I place the bottle in the center of my stove for about 20 minutes. The heat leftover from cooking (especially if you were baking) is enough warm the oil. This, in turn, loosens it up enough to collect at the bottom. Simlpy pour out the remaining oil.
A bottle that looks empty can give off as much as a few tablespoons of tasty oil. Enough to dress your next salad.