WP_Query () - meta_query OR tax_query

Question

I am trying to use WP_Queryto create a query with both an element meta_queryand an element tax_query. The kicker is that I do not want to find results in which both conditions are satisfied (and the AND clause). I want to find the conditions under which one or the other is fulfilled (OR clause).

So, I start with these arguments:

$args = array(
    'meta_query' => array(
        array(
            'key' => 'some-meta',
            'value' => 'some-value',
        )
    ),

    'tax_query' => array(
        array(
            'taxonomy' => 'some-taxonomy',
            'field' => 'slug',
            'terms' => array('some-term')
        )
    )
);

On run, WP_QueryI get this where clause (simplified here for clarity):

WHERE ( wp_term_relationships.term_taxonomy_id IN (336) ) 
    AND ( 
        (wp_postmeta.meta_key = 'some-meta' 
        AND CAST(wp_postmeta.meta_value AS CHAR) = 'some-value') 
    ) 

Is it possible to pass any argument to an object WP_Querythat will change this first AND to OR? I want it:

WHERE ( wp_term_relationships.term_taxonomy_id IN (336) ) 
    OR ( 
        (wp_postmeta.meta_key = 'some-meta' 
        AND CAST(wp_postmeta.meta_value AS CHAR) = 'some-value') 
    )