How would one then mount a light into that? I can't quite imagine it.
AHHHHH got it now...
I made my own. I'm going to paint it black to match my bike but all in all this only cost me a few dollars at the local hardware store:
that's a good design, but what's the advantage to that contraption over an undersided handlebar mount? the light is only going to be a few inches lower that the underside of the handlebars, where you could have a smaller, less obtrusive mount.
Main light mounted to fork crown:
I wonder about the nylon washer/spacer under your bracket. Was it just a need to move the bracket away from the headset or is it for you an optimal way of securing the bracket. Have you got already many miles with this and does it hold well?
Post 3 above is a close enough DIY interpretation.