Sugar cubes are added to a solution of water and lemon juice to make lemonade. The solubility of sugar is 200 g/100 g #H_2O# at the temperature of the solution. What can be done to increase the rate of dissolution without affecting the solubility?
Of course, heating is out, because a hot solvent will hold more solute than a cold one. What you could try is a sonicator, i.e. putting your flask in an ultrasonic bath. (These are very good for cleaning too!)