That's the way to use your head for something other than a hat rack!
Just add CalMAg and treat it like any other source of distilled water.
If your water needs rise, or your air humidity drops and you can't get enough from the dehumidifier, you can take UNSOFTENED well water and cut it by 50% with dehumidifier water to yield a solution at 200ppm, assuming that the hardness is from primarily dissolved limestone.