Basically this is the answer I was looking for from this question:
function yoastVariableToTitle( $post_id ) {
$yoast_title = get_post_meta( $post_id, '_yoast_wpseo_title', true );
$title = strstr( $yoast_title, '%%', true );
if ( empty( $title ) ) {
$title = get_the_title( $post_id );
}
$wpseo_titles = get_option( 'wpseo_titles' );
$sep_options = WPSEO_Option_Titles::get_instance()->get_separator_options();
if ( isset( $wpseo_titles['separator'] ) && isset( $sep_options[ $wpseo_titles['separator'] ] ) ) {
$sep = $sep_options[ $wpseo_titles['separator'] ];
} else {
$sep = '-'; //setting default separator if Admin didn't set it from backed
}
$site_title = get_bloginfo( 'name' );
$meta_title = $title . ' ' . $sep . ' ' . $site_title;
return $meta_title;
}