WordPress WooCommerce plugin featured images size different with the featured image

I am just developing an e-commerce site by using WordPress twentyeleven theme using WooCommerce plugin. Everything is working fine. But at one point I am struck. The demo site link is here.
In that site you can see Some of the product with some discount options in the all products section. For now I have made that static with simple html and css. Now I want that to pure dynamic so that admin can make changes. So to do that I searched about WooCommerce featured product and I got this link. Now with this link I just called the featured product in that area. But I faced the problem with the product image size. Now just below that you can see the images in the main page are 100X140. But for the featured image I need 500X75 image size. As I have gone through it, WooCommerce makes crop the same width and height for the featured product and the main product image. So can someone kindly tell me how to make the featured images into 500X75 and the images inside the main page should 100X140. Any help and suggestions will be appreciable. Thanks