Heat oven to 450°F. In bowl, place reserved strawberry juice. In another bowl, mix 1/3 cup of the sugar and the cornstarch; using whisk, beat into reserved strawberry juice. Stir in strawberries and rhubarb.
Remove pie crusts from pouches; unroll on work surface. Cut three 3 1/2-inch rounds and three 4 3/4-inch rounds from each crust. Firmly press each 4 3/4-inch round in bottom and up side of each of 6 ungreased 6-oz custard cups. Divide strawberry-rhubarb mixture evenly among custard cups.
Place one 3 1/2-inch round over filling on each. Seal crusts with crimp. Cut slits on top of each. Sprinkle with remaining sugar, dividing evenly among pies. Place custard cups in 15x10x1-inch pan.
Bake 32 to 36 minutes or until golden brown. Serve warm.