haha, there is a tool, but everyone has their own way of doing this.
i will start by leaving the accessory belt on and putting a good wrench on the hub, hit the end of the wrench with a good hammer to try and loosen it. one of two things will happen: 1- the hub will loosen and everyone is happy, 2- the waterpump pulley will slip on the belt.
If the pulley slips on the belt you have some options. i normally replace the belt while im in there so i dont really care if i damage it. I take a good size prybar and, with the belt still on (for extra grip), wedge it against the pulley to prevent it from spinning. it will take quite a bit of force, but it will work. the key is the sharp strikes on the end of the wrench with a hammer.
if you feel like it, a bit of heat on the nut never hurts... just be careful.