How can the boiling point of a liquid be raised without adding soluble impurity?

insoluble impurities donot raise the boiling point of a solution. it could be explained from raoults law that vapor pressure of the solution is affected by the partial vapour pressure of components in the solution.
         That is if the solute is not dissolved in a solution then how could it raise the boiling point. It wont affect its boiling point at all.