I've hacked my installation to give a slightly greater level of support. I'm sure someone can come up with a better way to do it:
In upload.php I inserted
$poc = urlencode( $piece_of_code );
directly before
$piece_of_code = htmlspecialchars( $piece_of_code );
and inserted
<a target="_blank" href="post.php?action=exact&content=<?php echo $poc; ?>"><?php _e('Create a new post with this image'); ?></a>
directly before
<strong><?php _e('Image Details') ?></strong>:
(both insertions are near the end of the file)
then in post.php I inserted
case 'exact':
$content = stripslashes($content);
# Intentional fall through
directly before
default:<br />
$title = __('Create New Post');<br />
require_once ('./admin-header.php');
This adds a link to the upload-completed page which creates a new post with the img link already inserted into the body.