Removing thumbnail from product.

I am using wp-ecommerce and I have big images that I am using for the main product image. Because of this I do not want the automatically created thumbnail because it is just showing the same image again. How would I just stop this automatically created thumbnail from displaying. I do have products with multiple images so I do not want to turn it off I just want to only show the thumbnail if I want to and this doesn’t seem to be an option. Any help would be appreciated.