If I'm reading his explanation right (and it worked on mine, so I think I am), it goes:

print safe """$subject - $poster on $date""";
var Link expand_link = $c->get_link("expand_comments");
if ($c.thread_url != "" and defined $expand_link) {
" " + $c->expand_link();

Where it says " " + $c->expand_link(); turn it into " " + $c->print_expand_link();

if ($comment.thread_url != "")
{
"""($*text_comment_thread) """;
var Link expand_link = $comment->get_link("expand_comments");
if (defined $expand_link) {
"(" + $comment->expand_link() + ") ";

It's the same for the "(" + $comment->expand_link() + ") ";

add the print_ before the expand_link and you'll be fine.