WP Display Header - helper function for single events

add_filter('wpdh_get_active_post_header', 'tribe_single_event_custom_headers');

function tribe_single_event_custom_headers($header) {
    // Bow out if a header was found or if this is not a single event query
    if (!empty($header) || !(is_singular() && tribe_is_event_query())) return $header;

    // Try to pull the actual single event post or bow out
    global $wp_query;
    if (count($wp_query->posts) !== 2 || !isset($wp_query->posts[0])) return $header;
    $event = $wp_query->posts[0];

    // Determine if we've got a specific header image to show
    $post_header = get_post_meta($event->ID, '_wpdh_display_header', true);
    return $post_header;
}