Step 1: Parts List
A picture is worth a thousand words and a video is worth even more. All of the instructions are demonstrated in the Instructional video.
You will need:
1. A peep hole - the kind you use on your front door to see who is on the other side. Get one at the hardware store. They come with 160 degree or 200 degree field of view. The 160 is probably fine for most wide-angle work. The 200 is as wide as most people will ever need. You can actually see slightly behind the lens with this one. And, it works better for fish-eye effect. However, is may show more barrel distortion. If you can't decide, get both.
2. PVC Pipe. The smallest diameter you can find that will fit around your camera's lens barrel.
3. Craft foam. These EVA foam sheets are available at craft stores and any place that sells scrap booking supplies.
Step 2: Build Up the Diameter of the Peep Hole Barrel
Measure and cut strips of the foam sheet. The width of the strips should be the same as the length of the peephole barrel. [Instructional video
Measure the length of the strips so that they wrap around the peep hole barrel.
Build up enough layers of foam so that the peep hole fits snuggly into the PVC pipe.
I used spray adhesive to glue the foam layers onto the peephole barrel and on to each other.
Step 3: Prepare the PVC Pipe
Cut a piece of PVC pipe to the length of the camera lens barrel plus the length of the peep hole
Paint the PVC pipe if desired
Step 4: Make the Camera Interface
Make a fitting for the camera lens by building up the thickness of the camera lens to fit the inside diameter of the PVC pipe.
Glue the resulting fitting inside the PVC pipe.
Step 5: Finish
I got best photo results when I had the camera lens zoomed in as far as possible.