You can try using a limited amount of reflected light onto the subject(s). That can make quite a difference on film. I have used pieces of cardboard covered with tin foil (the dull side) on one side. Worked alright, and it wasn't too bright. Generally, light from multiple directions works best to somewhat cancel out any unwanted shadows that suggest non-natural lighting.
EDIT: Dangit titaniumdoughnut, I was writing my post while you submitted yours...LOL.