I read somewhere that olive oil will solidify if you leave it in the fridge for a bit. So, I put a bit of first cold pressed oil into the refrigerator, and voila out came spreadable olive oil. Its not quite the same as margarine, but with a little bit of salt it could be adequate.
Make sure the oil you use says "first cold pressed" on the bottle. The oil is darker and greener than the cheaper stuff commonly used in cooking. First pressed oil comes from the initial pressing of the olives so has a great deal more flavor. This won't make any difference as far as solidifying is concerned, but the taste is so much better!