Problem with feature image being used as Directory thumbnail

I am using the Directory plugin to list several companies. I use the feature image to add the companies logos. Logos are always sent to me in small sizes and when I use them and then go to the individual listing the feature image is blown up on the top of the page by my current WP theme. It stretches the image and it looks horrible. How can I upload one (bigger) image for the feature image and another for the (smaller) thumbnail logo?

You can check out the problem here: http://avipla.org/directorio/adornos-ilu-s-a/