Flashlight shining up through a hole in a box that the jar is sitting in. Basically, that's it. I used the bathroom, as that's the only room in the house with no windows in it.
Your rheostat idea sounds brilliant. keep in mind that you should have a powerful bulb. As far as color temp goes, I think tungsten is easier to deal with than florescent. Experiment with screens and diffusion over the light source. I do not have to say "never forget the trusty bounce".