You might be better putting a light on your helmet, you'll have more choice too.
This is looking like the best suggestion.
I've got these, to give an idea of the space limitationshttp://www.dedaelementi.com/index.php?p ... 53&lang=en
Maybe something like this: http://www.evanscycles.com/products/smart/bracket-front-1-1-8-inch-threaded-headset-fitting-ec040100
It should allow you to mount most handlebar mounted lights to it.
Or perhaps something like this: http://www.topeak.com/products/Xtras/BarXtender
Neither is exactly pretty, but should work.
As for bright "see where you're going" lights, I just recently bought a Cateye Nano Shot Plus: http://road.cc/content/review/72875-cateye-nano-shot-plus-front-light
- plenty bright enough for completely unlit roads. It's expensive compared to some of the Ebay lights, but has the benefit of being an "all in one" unit that clips on and off the bike in seconds, rather than having a separate battery back and lense unit.
I really like that headset hanger for lights, that's a great idea, i wonder if it clears headsets? surely it must?
You could try this sort of thing that I built for my tourer - a 100mm length of 25mm aluminium tube secured to an SKS lamp bracket through the fork crown. Two lights with handlebar clamps then secure to the tube.
I really like your setup, what a great idea. However this is for my road bike so the front caliper is bolted through the forks and I'd be loathe to add anything else to it.