I made an extender out of a section of mtb handlebar and some old reflector mounts pieced together.

Handlebar extenders are probably the one thing that's easiest to make better than what you can get at a bike shop. The ones made by Minoura and (I think) Dimension are small and have no quick release capability (what if you want to take all of your lights and swap them from one bike to another at once. Or take them with you when you lock your bike). They are also very small.

I will try, however, fashioning one out of wood. That makes perfect sense.