Preheat oven to 400°.
In a metal mixing bowl, stir together sugars and cornstarch.
With an electric beater, thoroughly mix in eggs.
Add corn syrup and beat well.
Scrape down sides and bottom of bowl.
Beat in vanilla and margarine.

Meanwhile, place bowl of pie filling over simmering water.
Stir occasionally.
(The longer filling heats, the less time it takes to bake.)
Prick bottom and sides of partially thawed pie shell with tines of fork.
Place in preheated oven and bake until shell turns pale golden, 8 to 10 minutes.

Reduce oven temperature to 350.
Pour filling into partially baked shell.
Sprinkle pecans on top.
Bake, rotating if needed for even browning, just until set, about 30 minutes.
Serves 8.