a low-light idea
You could get one of these and just use the AF assist light http://www.amazon.com/gp/product/B00CXM03D2/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1
OK, tried that. There seems to be a snag: if you're using it in auto-ISO mode, you still have to hold down the Df "flash off" button, or it exposes as if it were about to take a flash picture (that is to say, grossly underexposes, since you're not using flash). Also, the ABC lights on the right of the unit flashed continually -- is there a way to stop that? -- annoying in dark places.