One way this can be achieved, without resorting to custom page meta inputs, is to simply enable support for excerpts on pages.

The excerpt content section that is visible on the post edit screen will then be displayed on the standard page content editing screen.

This can be achieved very quickly and easily by including the following lines in the theme functions.php file:

    // Enable excerpts for pages...
add_action('init', 'enable_page_excerpts');
function enable_page_excerpts()
{
    add_post_type_support('page', 'excerpt');
}

There are a few downsides to using this method, so it is advised that you use with caution.

Although it wasn’t immediately obvious to me, read more links can be enabled by over-riding the global $more variable and setting it to false, before looping through the result set, for example:

global $more; $more = FALSE;
query_posts('post_type=page');
if ( have_posts() ) : while ( have_posts() ) : the_post();
	the_content('Read More...');
endwhile; endif;

I couldn’t actually discover why this is not the default behaviour when querying pages. There may be a good reason behind it, but in my experience I found it mildly irritating.