We don't really have much in the way of tree skiing around here, especially by Big Sky.
Your best bet for good filmable lines would be either a-z chutes as mentioned before (I'll be really surpised if they're skiable then), the headwaters at Moonlight (never has good light), or maybe the couloir, but that probably wouldn't be a very good run to film. I think Bridger has a lot cooler terrain to film, but if you're just skiing Big Sky there' some sweet stuff up there as well--conditions permitting.