I noticed this was not resolved, although I’m sure the Plug In works fine.
Here’s my solution without using a Plug In:
After locating where the default pictures were stored, I found the images and the thumbnails:
../wp-content/themes/twentyeleven/images/headers/
I created my new header as a JPEG, sizing it to be 1000 wide and the smaller custom height. I also created a thumbnail, the same size as the ones I found in the directory.
I named the header thumbnail “willow-thumbnail” and the header “willow”.
I copied my new JPEGS into the directory, replacing the default “willow” photos.
Using the Dashboard, Appearance, Header menu, I picked my new short header. It worked great!
The only downside was on upgrade I expect I’ll have to copy the picture in again. Today when I made my child theme and switched to it, I did have to choose the header photo again.
My fix is done for now, however, I did notice the Plug In listed here which would good to try as well.