Secretly passing post ID/title etc into a shortcode form automatically to link submission to post

If you put a unique placeholder value there, you can do a find/replace via the_content filter, which runs after the shortcode is rendered, but before the content is output in the template.

For example, this will replace any occurrence of replacethisthing with the post ID:

function wpd_replace_something_in_the_content( $content ){
    return str_replace( "replacethisthing", get_the_ID(), $content );
}
add_filter( 'the_content', 'wpd_replace_something_in_the_content', PHP_INT_MAX );