Product with multiple variable attributes

I am setting up a ecommerce site for photography. I am trying to use variable product types to be able to offer a print in various sizes, various finishes (no extra charge), a matted option and a framed option. The variable product works great with just a size attribute and no extra charge for the finish. When adding any additional attribute, I am not able to add just a cost for that attribute. How can you offer a product with four variable attributes whithout having a price for each possible combination of attributes?

http://ww.wp.xz.cn/extend/plugins/woocommerce/