WordPress SimplePie Modifications

I am using the fetch_feed() function provided in WordPress to build a SimplePie feed object.

The code from WP is the following:

function fetch_feed($url) {
require_once (ABSPATH . WPINC . '/class-feed.php');

$feed = new SimplePie();

$feed->set_sanitize_class( 'WP_SimplePie_Sanitize_KSES' );
// We must manually overwrite $feed->sanitize because SimplePie's
// constructor sets it before we have a chance to set the sanitization class
$feed->sanitize = new WP_SimplePie_Sanitize_KSES();

$feed->set_cache_class( 'WP_Feed_Cache' );
$feed->set_file_class( 'WP_SimplePie_File' );

$feed->set_feed_url($url);
$feed->set_cache_duration( apply_filters( 'wp_feed_cache_transient_lifetime', 12 * HOUR_IN_SECONDS, $url ) );
do_action_ref_array( 'wp_feed_options', array( &$feed, $url ) );
$feed->init();
$feed->handle_content_type();

if ( $feed->error() )
    return new WP_Error('simplepie-error', $feed->error());

return $feed;
}

How can I modify which HTML elements get stripped during the feed import?

SimplePie in its documentation says that there is a function strip_htmltags(), but I’m not sure how I can use it within the WordPress context. http://simplepie.org/wiki/reference/simplepie/strip_htmltags