That would require the user to upload a different header images for each top page and category. I can’t see a neat solution for that, nor do I see strong reasons why most people would need that kind of functionality.
Additionally, the theme already supports alternate header image for individual posts and pages. You can use the Featured Image function to replace the header image on individual posts and pages. Just make sure that the image you set as the Featured Image has a dimension greater than or equal to the header image size.