Shred pear; place shredded pear pulp on several layers of cheesecloth. Gather edges of cheesecloth together, and squeeze over a glass measuring cup to yield 1/3 cup fresh pear juice. Discard solids. Combine pear juice, vodka, pomegranate juice, lime juice, and agave syrup in a cocktail shaker with ice; shake. Strain about 3 tablespoons of the vodka mixture into each of glass. Add cider and top with sparkling water. Garnish with pear slices, if desired.