Place the lime zest and sugar in the bowl of a food processor and pulse until finely ground. Measure out 1/4 cup mixture and transfer the rest to a shallow dish. Pour 2 Tb lime juice in another dish. Dip the rims of 4 glasses into lime juice and then into zest mixture. In a blender puree the nectar with the rum and remaining lime juice and zest mixture. Pour into prepared glasses and serve.