Bring first 3 ingredients to a boil in a heavy saucepan, stirring constantly; boil 5 minutes. Add pear and lemon rind; return mixture to a boil, and cook, stirring occasionally, 3 minutes. Stir in cranberries. Reduce heat, and simmer, without stirring, 3 to 5 minutes or until cranberries pop. Remove from heat; cool. Cover and chill.
Remove ginger; chill sauce up to 2 days. Stir in lemon juice just before serving.