Heat 1 cup of the reserved syrup and the sugar to boiling, stirring constantly; remove from heat.
Place pears, half at a time, in blender container; cover and puree until uniform consistency.
Mix syrup, puree, lemon juice and ginger; pour into ice cube tray.
Freeze until partially frozen, 1 to 1 1/2 hours.
Pour into blender; blend on medium speed until smooth and fluffy.
Return to ice cube tray.
Freeze until firm, about 3 hours.
Let stand at room temperature about 10 minutes before serving.