Hi,
When doing a large import i would suggest disabling the addon and then re-enabeling after.
The system checks when a post previously not having the status of pusblsh then goes to publish, it then copies the ID and title to a WP option
get_option( 'gdfi_post_to_facebook');
You could do your manual way many ways but a simple way would be to update the option with an array of your posts you want publshed (i would not do more than a few at a time as it will run the next time someone visits the frontend of your site so could cause a long wait for someone.
EXAMPLE CODE, NOT TESTED:
$my_posts = array(
array('ID'=>123,'title'=>'the post title for 123'),
array('ID'=>124,'title'=>'the post title for 124'),
array('ID'=>125,'title'=>'the post title for 125'),
array('ID'=>126,'title'=>'the post title for 126'),
);
update_option( 'gdfi_post_to_facebook',$my_posts);
Stiofan