1.Combine sugar and water in a small saucepan.
2.Cut ginger into 5mm slices; cut slices into thick strips. Add ginger to saucepan; stir over medium heat, without boiling, until sugar dissolves.
3.Bring to the boil; boil for 5 minutes. Transfer to a heatproof jug; cool. Add lime juice and vodka to jug; cover and refrigerate until ready to use.
4.Pour 2 tablespoons of the ginger vodka mixture into 8 chilled glasses; add a couple of pieces of the cooked ginger and a few slices of lime. Top with sparkling wine just before serving.
5.Serve with oysters on a bed of ice.