Combine 1/3 cup rum with pear juice and sugar in a 10-inch heavy skillet and bring to a boil, stirring occasionally. Reduce heat, add the raisins and pears, and simmer, covered, until pears are just tender, about 10 minutes. Remove the lid from the pan and using a slotted spoon, remove the pears to a plate. Boil the poaching liquid, stirring occasionally, until liquid is reduced to a syrup, 5 to 10 minutes. Stir in the butter and the remaining tablespoon rum and return the pears to the pan. Serve over frozen yogurt.