It's not perfect, but it's close.
If you edit the style.css file so that the header size is 980px x 200px(or whatever you want) instead of 20px, it will give you room to create your custom header. Then replace the header-back.png file in templates>default>images with your header and it will work.
You may have to create tiny strips of your background color on the sides of the header to match the background. It's not perfect but it works.



