Cut 20x18-inch sheet of heavy-duty foil. Cut frozen cake horizontally into 4 thin slices; place bottom layer lengthwise on foil.
Spread 1/4 cup of the ice cream topping over bottom layer. Spoon 1/3 of the ice cream over topping; smooth top. Repeat layers twice and top with remaining cake slice, pressing cake firmly.
Wrap tightly in foil; freeze until firm, about 4 hours. To serve, cut into slices.