How can I return shortcode output to the top of the content?

Question

A cleaner way than my first suggestion would be this:

Run the shortcode handler two times: 1. before the content is parsed, 2. during the regular content parsing.
Store the data you want to prepend in a variable.

It is important to use 'the_post' as first entry. Otherwise you can get strange side effect in cases where a widget or some other code uses the_content filters.

add_shortcode( 'test',  array ( 'WPSE_77804_Shortcode', 'shortcode_handler' ) );
add_action( 'the_post', array ( 'WPSE_77804_Shortcode', 'store_output' ) );

class WPSE_77804_Shortcode
{
    protected static $storage="";

    public static function store_output( $post )
    {

        // maybe someone else has done this already, so we don't have to try again.
        '' === self::$storage && do_shortcode( $post->post_content );

        '' !== self::$storage
            && add_filter( 'the_content', array ( __CLASS__, 'prepend_content' ) );
    }

    public static function shortcode_handler( $attrs, $content="" )
    {
        if ( '' === self::$storage )
        {
            if ( isset ( $attrs['title'] ) )
                self::$storage .= $attrs['title'];

            if ( isset ( $attrs['date'] ) )
                self::$storage .= ' ' . $attrs['date'];
        }

        // you might do much more here and return the complete string
        return '|' . self::$storage . '|' . $content;
    }

    public static function prepend_content( $content )
    {
        return self::$storage . '<hr>' . $content;
    }
}