add_filter('the_posts', 'bump_sticky_posts_to_top');
function bump_sticky_posts_to_top($posts) {
    foreach($posts as $i => $post) {
        if(is_sticky($post->ID)) {
            $stickies[] = $post;
            unset($posts[$i]);
        }
    }
    return array_merge($stickies, $posts);
}