Unfortunately, I'll have to let others answer that, as my JS skills are minimal. It's probably the way that script you are using is designed to work ... which makes it kind of faulty, if you ask me. But I realize you chose it partly for its functionality, and unless you are a JS ace, you usually have to accept what you get in these cases.
Personally, I would build that page manually jut with HTML and a bunch of thumbnails that enlarge once clicked, but that's not what you want for this page, I realize. I hope someone with JS skills can help you here, but if not—and if this functionality is really important for the site—the best thing would be to hire a programmer to write a script that does just what you need in an efficient way.