I solved my requirement as follows.. i edited the nextscipts_snap.php and added the following conditional lines into nsFormatMessage function.

It is working properly but the problem is i have to update the code each time i updated the script.
I hope there will be a feature for custom fields soon.


if (preg_match('%MYMSG%', $msg)) {
$recipe = get_post_meta($postID, 'mycustomfield', true);
if ($recipe!="") $excerpt = $recipe; else $excerpt= "";
$excerpt = nsTrnc(strip_tags(strip_shortcodes($excerpt)), 300, " ", "..."); $msg = str_ireplace("%MYMSG%", $excerpt, $msg);
}