Hmm...
You could film in a light, brighter than what you currently are, and in post or in-camera darken it.
You could set up a few soft lights and use reflectors to reflect on the actors a soft light with no shadow...

"Video's a poor excuse, I know. But it helps me remember... and I need to remember... Sometimes there's so much beauty in the world I feel like I can't take it, like my heart's going to cave in. "

as oleg said you can light it softly then darken it in post by taking away whites and using some blues and purples or yo ucan find lights that give off a blue tint. The blue tint makes things look darker then they really are. If you have ever seen The Ice Harvest then you see an example of this when in the beginning right after they take the money and are in the car talking. The scene was actually shot during the day but they reflected alot of the natural light then darkened it in post. This was also done in Wolf Creek in some scenes.

"Anyone who has ever been privileged to direct a film also knows that, although it can be like trying to write 'War and Peace' in a bumper car in an amusement park, when you finally get it right, there are not many joys in life that can equal the feeling." - Stanley Kubrick

I just had to shoot something like this for my feature. What I ended up doing was bringing in a lot of strong, directional light to create harsh shadows, then I tinted it slightly blue and darkened it a bit in post.

How you light this really depends on what kind of look you're going for, but one thing to try is lighting the scene as if it is being illuminated by the moon or a lamp or night light or something.

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Andrew Gingerich
Exploding Goldfish Films
Check out my vodcast on iTunes: http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewPodcast?id=96931870