If your theme doesn't have a section of the dashboard for CSS modifications, e.g named "Custom CSS" then install this plugin: http://wordpress.org/plugins/custom-css-manager-plugin
Then use that plugin's section of the dashboard to hold your CSS modification that will put a header image behind your title and description:
Is there a way to add this as an option for single pages? I would really appreciate that!
It's not necessarily an option in the theme but you could precede your '
#header' class with the single template class. That class should appear in the '
<body>' element on your single page's source code if you want to explore what it is.