In a small saucepan, heat sugar and 1/4 cup pear brandy over moderate heat until sugar is dissolved, about 5 minutes. Remove pan from heat and cool syrup. Spoon 1 1/2 tablespoons syrup into each of 4 champagne glasses and add 1 teaspoon pear brandy to each glass. Add 2/3 cup champagne to each glass and stir well. Cut pear lenghtwise into thin slices and add 1 slice to each cocktail.;