In answer to the original question, you can pass attachment IDs to the gallery by through an exclure parameter, i’ve posted a blog on how to do it:
http://creativebinge.co.uk/blog/wordpress-excluding-featured-image-from-gallery/
or here is the code (placed within a single-post) file:
< ?php echo do_shortcode('[gallery size="full size" exclude="' . get_post_thumbnail_id( $post->ID ) . '"]'); ?>
