I think some reflectors are the answer here. Try taking two or three pieces of white mounting or poster board and setting it so that it bounces your light back into the scene. The trick is to get them close enough without interfering with the set up. You can also take one of these and trace the circle of your lens, cut it out and then slip it over the lens. This will do a couple of things for you. First if yu are close enough, it will act as a reflector and add light to the scene. Second, if it is large enough, it will allow you to shoot closer without the camera being picked up in the mirror (possibly... depends on the angle). Hope this helps :)