I use WP Hive plugin to have multiple blogs with same core files.
"If you don't want rotating header images, leave only one image in that directory."
I have 2 (or more) blogs with Atahualpa theme and I want separate header image to use but they use the same files.
In the source there is support to WPMU [function bfa_rotating_header_images()] but its not an option for me.
It will be great to have an option in the header image setting to put the exact url for the header image even if thats not in the /images/header directory.
e.g.: great job with the theme!