Custom header – random header image

Hi,
On the Custom header – header image section of site configuration (wp-admin/themes.php?page=custom-header) I currently use the option to choose a random image from a collection of uploaded images.

I’d like to be able to select all or some of the images from which the random choice is made. Typically the images may be seasonal and I no longer want to use the winter images – but I don’t want to delete them!

Thanks
Patrick