In a WP_Query can I force the results’ is_singular() to be set to false?

If you really think the is_singular() function of your query should be returning true for singular but isn’t, you can force it to be true by setting the public property is_singular directly after the query, since that function just returns the value of that property when no $post_types parameter is specified:

$the_query = new WP_Query($args);
$the_query->is_singular = true;

Or if you need to do so for the main query:

global $wp_query;
$wp_query->is_singular = true;

I can’t speak to the wisdom of whether or not this should be done—it probably depends largely on your implementation—but it can be done since that property is public.