use gallery ids to output however you want.

gallery-id-grabber

// into template or another filter i suppose

$pattern = get_shortcode_regex();

if( preg_match_all( '/'. $pattern .'/s', $post->post_content, $matches )
    && array_key_exists( 2, $matches )
    && in_array( 'gallery', $matches[2] ) ):

        $keys = array_keys( $matches[2], 'gallery' );

        foreach( $keys as $key ):
            $atts = shortcode_parse_atts( $matches[3][$key] );
                if( array_key_exists( 'ids', $atts ) ):
                    $thumbs = array();
                    $images = new WP_Query(
                        array(
                            'post_type' => 'attachment',
                            'post_status' => 'inherit',
                            'post__in' => explode( ',', $atts['ids'] ),
                            'orderby' => 'post__in'
                        )
                    );

                    if( $images->have_posts() ):
                        // loop over returned images
                      var_dump();
                      foreach($images->query['post__in'] as $id) {
                        $full   = wp_get_attachment_image_src( $id, 'full' );
                        $thumb  = wp_get_attachment_image_src( $id, 'map-thumb' );
                        echo '<li>';
                        echo '   <img src="'.$full[0].'" />';
                        echo '</li>';

                        $thumbs[] = $thumb[0];
                      }
                    endif;

                    wp_reset_query();

                endif;
        endforeach;

endif;


// into functions.php
function my_gallery_shortcode( $output = '', $atts, $content = false, $tag = false ) {
    return '<div class="clear"></div>';
 }
 add_filter( 'post_gallery', 'my_gallery_shortcode', 10, 2 );