Is it possible to use WP_Query to query posts by checking for a match in the title OR a custom field

I strongly suspect the answer is 'no', and that I'll need to construct a custom SQL query, but I'd like to check as a last resort because using $args and WP_Query is so much neater...

If I have a text string $searchstring and look to construct a query like this:

$args = array();
$args['post_status'] 	= 'publish';
$args['s'] 	= $searchstring;
$args['meta_key'] = 'intro';
$args['meta_query'] = array(
	array(
		'key' => 'intro',
		'value' => $searchstring,
		'compare' => 'LIKE'
	)
);

and then try to get to a result with
$search_query = new WP_Query( $args );

the query will look for posts which match BOTH of these:

(1) the text string $searchstring is in the post title
(2) the text string $searchstring is somewhere in the value for custom field 'intro'

I want to look for posts which match one or the other of the above 2, not necessarily both.

Is this possible without having to construct a custom SQL query string?

Any help or hints would be greatly appreciated.

Thanks,
Shaun