fzstudios

Look for the images_from_wpgallery function within the WPSupersized.php file. Within that function you’ll see a get_children array
Exclude the get_post_thumbnail_id() at the end of the array, i.e.:

$images = get_children(array( // gets images attached to the post/page
		'post_parent'    => $postid,
		'post_type'      => 'attachment',
		'numberposts'    => -1, // show all
		'post_status'    => null,
		'post_mime_type' => 'image',
		'exclude'     => get_post_thumbnail_id(),
                                ));

This worked for me.