1. create a folder called wp-content/header-images/
2. in ATO/ Style and Edit Header Area delete %image
3. Install Dynamic Headers
4. Under settings on the dashboard there is now a section called Headers, upload your pre-sized custom banners
5. Set a default image if you want or allow images to be random
6. Take the line of php code they give you and throw it into header.php
And it works perfectly!