Are you using the whipping cream as a topping or as a substitute for cream
in the pie?  If you are using it in the pie I have used soy milk in place of
cream in pumpkin pie recipes and it turns out great.

If you are wanting a whipped topping, I found a frozen one (similar to Cool
Whip) that I plan to try this weekend.  I found it at a local health food
store, but can't comment on the quality since we haven't tried it yet.  It
is called Hip Whip by Now and Zen.  Ingredients are:  Water, grape juice
concentrate, expeller pressed high oleic canola oil, cocoa butter, tofu
(soybeans, calcium sulfate), brown rice syrup, cashew butter, agar agar,
pure vanilla extract, guar gum.

I also have a microwave recipe for dairy-free chocolate pudding which would
be very good in a pie if you want to try this.

Chocolate Pudding

1 Tbsp. margarine
2 squares unsweetened chocolate (or 6 Tbsp. cocoa and 2 Tbsp. oil or
shortening)
1/2 cup sugar
3 Tbsp. corn starch
1/4 tsp. salt
1 3/4 cups soy milk or other milk substitute
1 egg, slightly beaten
1 tsp. vanilla or almond extract

Combine margarine and chocolate.  Microwave 45 seconds to 1 minute on high
until melted.  Set aside.

Mix sugar, corn starch and salt together.  Gradually stir in milk
substitute.  Blend in melted chocolate mixture.  Microwave 6-7 minutes on
"8", or until thickened, stirring once with a wire whip.

Stir a little of the hot mixture into the egg.  Blend warmed egg into hot
mixture.  Microwave 1 minute and 30 seconds on "8", or until custard coats a
metal spoon.  Fold in vanilla.  Cool.

I hope that some of this helps you.

Sandy