Post meta entries are in your wordpress database, in the wp_postmeta table.
I am just a newbie, not sure if this is right, but something I can think of that might help you in the right direction. Hope this helps.
function wordpress_custom_post_meta_bulk()
{
$posts = get_posts(array('numberposts' => -1) );
foreach($posts as $p) :
$meta += array('_key' => '';
'_value' => '';);
update_post_meta($p->ID, 'meta',true);
endforeach;
}