We are renting a 1.2K HMI PAR and 12x12 silk. In addition to that, some of our larger sources are 2K fresnels and a 2K softlight. My gaffer was thinking that we would do a hard backlight with the HMI and then bounce that light back at the faces. If, as you said, the stock is going to react more strongly to the HMI, I think we should be in good shape. We also do have some fog machines that we weren't originally intending to use on the road, but now I'm beginning to think that a little fog could be very useful.
In response to your suggestion, inder mann, I had considered shooting at twilight, but I don't think we'll have enough time. If we get into a pinch though, I thought about shooting during the day, underexposing, and possibly using a polarizer to bring the sky down. Does that sound like something that would be reasonable to do?