While this was far from clear in the OP at first, I think this might be a good solution. Just make a shortcode to place the excerpt in the body. (This is a bad idea if you want this on every page. This is a good idea if you want it once in a while on some pages in the body.)
Here’s code to put in your functions.php:
function the_excerpt_shortcode() {
return get_the_excerpt();
}
add_shortcode( 'the_excerpt', 'the_excerpt_shortcode' );
Once you have the, just put this in your page body:
[the_excerpt]
And you’re good to go.
If you’re using Twenty Ten, Twenty Eleven, or some other theme that hooks to the excerpt_more filter, you may have to modify that short code to strip an auto-generated “Continue Reading…” link, but for many themes that’s unnecessary. Consider this a starting point.