Here it is... Nothing real special, but it works and I figure it cost around $.06 to make, about 1 square foot of aluminum foil, a cardboard cereal box, and a few pieces of tape.
It's lasted about 5 outings so far, but it's getting a bit wobbley now. Some tape reinforcement may be needed, but I may try to make a collapsable version out of some white foam board or perhaps some scraps of matboard later, maybe it will be sturdier.
In practice, the top end actually bends down slightly more than shown here.
a back view. Note the high-tech fastening mechanism...
When I'm using one of the longer lenses, like the 150 f/3.5 with extension tubes, I'll hook up my wireless trigger (the strobist el-cheapo's, $30) - and hold the flash where I want it. When I was shooting the bugs with the 40mm, I had it mounted on an inexpensive L bracket with a sync cord attached, and occasionally I would detach it from the bracket and move it around by hand to vary the light.