WP_Query: How do I sort on meta value and use LEFT JOIN?

I use WordPress 4.5 and I am trying to modify a query to use LEFT JOIN instead of INNER JOIN. But I cannot get 'relation' => 'OR' to work. See the query below. I have read a number of other posts about this but I cant get it right.

$premium_args = array(
        'meta_query' => array('relation' => 'OR', array( 'key' => 'premium', 'value' => '1', 'compare' => '=' )),
        'tax_query' => array( array( 'taxonomy' => 'posts-from', 'field' => 'id', 'terms' => $term->term_id ) ),
            'post_type' => 'post',
        'posts_per_page' => $posts_per_page,
        'meta_key' => 'verified',
        'orderby' => 'meta_value_num',
        'order' => 'DESC',
        'paged' => $paged
    );
    $premium = new WP_Query( $premium_args);

Below is the query result. How can I force it to use LEFT JOIN?

REQUEST:SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  INNER JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id) INNER JOIN wp_postmeta ON ( wp_posts.ID = wp_postmeta.post_id )  INNER JOIN wp_postmeta AS mt1 ON ( wp_posts.ID = mt1.post_id ) WHERE 1=1  AND ( 
  wp_term_relationships.term_taxonomy_id IN (7)
) AND ( 
  wp_postmeta.meta_key = 'verified' 
  AND 
  ( 
    ( mt1.meta_key = 'premium' AND CAST(mt1.meta_value AS CHAR) = '1' ) 
    OR 
    ( mt1.meta_key = 'verified' AND CAST(mt1.meta_value AS CHAR) = '1' )
  )
) AND wp_posts.post_type="post" AND (wp_posts.post_status="publish" OR wp_posts.post_status="private") GROUP BY wp_posts.ID ORDER BY wp_postmeta.meta_value+0 DESC LIMIT 0, 25

WordPress is also provide more filters to change custom queries.
https://codex.wordpress.org/Custom_Queries

add_filter('posts_join', 'custom_query_join' );
$premium = new WP_Query( $premium_args);
remove_filter('posts_join', 'custom_query_join' ); // remove filter bcz not effect to another query to use after this query.

function custom_query_join( $join ){
  $join .= 'Put here join to table';
  return $join;
}