Editing core file: SimplePie parsing chokes on entity

I need to consume an RSS feed being generated by ColdFusion which occasionally contains a malformed entity. Fixing all the input isn’t an option.

It works when I add this function to class-feed.php:

function stripInvalidXml($value)
{
    $ret = "";
    $current;
    if (empty($value))
    {
        return $ret;
    }

    $length = strlen($value);
    for ($i=0; $i < $length; $i++)
    {
        $current = ord($value{$i});
        if (($current == 0x9) ||
            ($current == 0xA) ||
            ($current == 0xD) ||
            (($current >= 0x20) && ($current <= 0xD7FF)) ||
            (($current >= 0xE000) && ($current <= 0xFFFD)) ||
            (($current >= 0x10000) && ($current <= 0x10FFFF)))
        {
            $ret .= chr($current);
        }
        else
        {
            $ret .= " ";
        }
    }
    return $ret;
}

And then add a call to it before parsing in the class declaration in the same file:

class WP_SimplePie_File extends SimplePie_File {
//bunch of code
$this->body = stripInvalidXml(wp_remote_retrieve_body( $res ));
//rest of function
}

I’d like to extract these changes so they won’t break on the next update of WordPress, but simply overriding the class in functions.php seems unlikely to do what I expect. I could write my own class with a slightly different name..but I’d still have to change the core files to call that instead of WP_SimplePie_File, so it only moves the problem.

What’s the right way to do this? Also, since SimplePie seems to be dead, is there an up and coming approach to RSS I should be aware of? Is this all going to break in a soon-to-be version anyway?

Thanks!