White reflectors are a good idea...but also don't be afraid of wide apertures. You can handhold a rangefinder at a much slower speed than many other cameras. Of course, you're not going to get depth of field at those apertures but you will gain a wonderful glow.

Here's one at f2.0, a Zeiss Planar 50mm on a Leica M2...scan of a silver print.

http://www.flickr.com/photos/viapiano/2547066661/