South Dakota, huh? That explains everything 
I looked all over the strobist site to find an example (maybe I saw it on another site), but a very cool shot I've seen was done at twighligh, with all of the lights on inside the building, and a strobe lighting the group about 30ft in front of the build (but I'm starting to think that they did this because the building was pretty bland, not like the one you have).
If you have the OneLight DVD, look where he lights the girl in the alley, by the building. If you don't have it, look for the teaser on youtube. Theres a sweet shot of a girl in a scarf (I think) where the building is underexposed. It's pretty sweet. Of course, lighting a dozen people just complicates things.
Do you know what they're wearing? Suits? Casual stuff?
The only idea I can think of for posing is to arrange them around one of thier yard signs. Maybe a couple down font. Sunglasses might be cool.
Try to find out what the "feel" of the ad is going to be (and any text). That might help you get the feel of the photo.