My rough calcs estimate you would need about 400mg of salt per ml of water to get a 7°C boiling point increase, but the max solubility of salt in 100°C water is

My rough calcs estimate you would need about 400mg of salt per ml of water to get a 7°C boiling point increase, but the max solubility of salt in 100°C water is 384mg/ml, so you might just get there with a supersaturated solution. Can sous-vide machines hold 100°C in oil?