If I'm not mistaken it has been fixed. I have an older Holga 120 in which the aperture doesn't seem to change and a new Holga 120 which does seem to change.

I love the gel idea. I saw a YouTube video which shows how to disassemble a Holga 120 and it looks pretty easy. I believe there are four screws inside the camera that hold the lens mount in place and one screw that keeps the lens from being unscrewed from the mount when rotated. Though I've never taken any of my four Holgas (I know, it's a sickness) apart.