Any advice for lactose-free sour cream sub? Half my family is lactose-intolerant and I would love to make this pie! Will be using the coconut milk...

I have made cashew sour cream before and it is great on salads. You could try one of those recipes. A warning though, some can be quite thin and you will need a faux sour cream that is somewhat thick yet still moist. I would try one of these two recipes and add liquid as necessary. http://www.therawtarian.com/raw-sour-cream-recipe or http://www.wholefoodsmarket.com/recipe/cashew-sour-cream

I don't know if anyone's ever thought to sell this yet, but a sourcream-like substance can be made from coconut milk kefir (would possibly contain traces of milk depending on the kiefer strain and how it's cultured). Of course, it's too close to thanksgiving to get the kefir grains... but for future holidays it might be an option.

In the book Vegan a Go Go by Sara Kramer (I love this book for allergy substitutions as many of her recipes actually taste like what they are replacing), she has a recipe for 'faux sour cream' that uses Tofu, and other common pantry ingredients. 'Though Kramer doesn't say if her Faux Sour Cream will hold up to being baked, it looks to me like it would.

In other news... there is lactose-free yoghurt?!?! Why has no one told me this before? That's fantastic news and would definitely be my first choice for substituting in this recipe. ... then again, some people with severe lactose sensitivities can still react to lactose free milk (I suspect they are sensitive to the proteins in the milk instead of/as well as the lactose) so best to ask them first if the yoghurt would be okay.

Are you able to easily get soy sour cream or soy yogurt where you are? Either of those would be my first choice for replacing. Coconut cream might be a good option too, but combined with the coconut milk you'd definitely have a pronounced coconut flavor in the pie.

You could try using a dairy-free sour cream (like the Tofutti) brand or a lactose-free yogurt. Otherwise, I imagine you could just substitute 1 cup total of coconut milk for both the heavy cream + sour cream.