Reakon on "Reply to comment on single comment page"

Dear,

At this moment I am working on a comment system for one of my clients but I am running into a problem.

The comment system has some additions to it, since the comments are 'concepts, ideas & inspirations' - kind of crowdsourcing community.

Anyways, I now have: the comment excerpt a image and the title on the normal page, with a link to the bottom 'See more' (Zie meer in dutch).
When clicking on this link you're brought to a another page where the whole comment can be seen (images, story, etc).

I do this as following:

<a href="single-comment/?id=<?php echo comment_ID(); ?>&auteur=<?php comment_author(); ?>&pageid=<?php echo get_the_ID(); ?>">See more</a>

Then I pull the comment ID & the page ID from the link (the author is there for SEO reasons).

if(isset($_GET["id"]) && isset($_GET["auteur"]) && isset($_GET["pageid"]))
    {
     $commentid = $_GET["id"];
     $auteur = $_GET["auteur"];
     $page_id = $_GET["pageid"];
    }

$comment = get_comment( $commentid );

But now my client had the question; can people reply to a 'idea, concept or inspiration added by another user' - this 'ideas, concepts or inspirations' are technically seen comments.

So I tried to add a 'reply to' link:

$commentreply = get_comment_reply_link(array_merge($args, array('depth' => $depth, 'max_depth' => $args['max_depth'])), $comment->comment_ID);

but when I 'var_dump' this... it says: "NULL".

Anyone an idea how to make this kind of comment system?