Hello. My theme, Twenty Eleven, allows me to use random images for my header. I like that, but I want to choose the random images myself. In other words, I want to upload several of my own images and have the theme randomly select which of them to use (changing every time someone reloads the page). But the header page seems only to allow me to use Twenty Eleven’s default themes. Does anyone know how to fix that, or if it’s even possible?