The item I used for my diffuser was a cheap $3.00 project box, obtained from a local Radio Shack. I removed the 9v battery compartment lid, took out the screws and cut out a larger area as shown below.
Step 2: Diffusion
For the diffusion material I cut a properly shaped piece out of a 4litre water jug. and replaced the open end piece of the project box with it.
Step 3: Putting it on the Camera
Simply slide the box over the top of the on-board flash (while it is open) and if you cut it right, it should hold in place over the back of the HOT SHOE.
All Done, it looks oddly familiar.......
Step 4: Testing it out
Putting it to the test... I would say it's a success.