Do you mean that you want someone to be able to order one item in any one of a selection of sizes? You could do this before.
Do you mean that you want someone to be able to order one item but in two or three sizes (like say, the listing is for a discounted rate for 2 shirts and you want them to be able to pick 2 different sizes for the shirts) - this you can do, and could before. Only 2 sizes, though, as there are only 2 variations.
