I doubt the camera will get much smaller or lighter without the case. I haven't tried mounting one in a 2.6" tube, but in my 4" rockets I've just had the camera stick out the side of the rocket. That way you you have the option of positioning the camera so that it looks down the side of the rocket or straight out.
For the latest camera carrier, I scrapped the fancy way I used to mount the camera and basically just cut a hole in the side of the rocket. I made a platform in the rocket that the camera sits on then, after starting the camera right before launch, I use a wrap of electrical tape around the camera and platform to secure it. Then I put on the nose cone that's held on with a couple of small screws.
The eletrical tape works well because, if the camera tries to escape, it holds on tighter. If you don't want the sticky residue left on the camera after the flight, wrap the camera in a little plastic wrap first.
The above isn't a great photo of the setup, but it's the only one I can find right now. The camera in this case is actually a Panasonic SDR-S10, but it is about the same size as the AIPTek camera.
I had to mount the platform about half-way inside the 4" tube. So, I think mounting the camera against the other side of the tube with no platform might work for the 2.6" tube. You might cut slots or create something inside the tube to use to anchor the electrical tape (or whatever other mounting method you use). You might line that section of tube with a couple to beef it up since it'll have a big section cut out.
-- Roger
