I made this a while ago just really to see if the idea would work....and it turned out it does, quite well in fact.
The pics hopefully explain it better than I can in words, but basically its a tubular extension that slips over the onboard flash. It`s made from thin flexible plastic (from a large milk carton)with the inside lined with tin foil to reflect the flash along it.
I made it with 2 layers, to sandwich a couple of lengths of flexible wire between them to firmly adjust the angle of the reflector at the end so it drops light where required.
It`s pretty rough in construction, I intend to make a better version soon.
It will adequately light subjects down to around 6 or7 cms from the front of the lens, and that`s with a Permaraal 55mm adaptor fitted to the camera too.