I think that I would be hesitant in doing this if a customer asked me to make this happen. I know I could but the liability down the road would cause me nights of unsleep.
But if you had to, I would condense the channels down real close in the fan area. And I would hang much much more hanging wire all around the area where the fan is intended. Look around in the Home Depot's and see how they hang their heavy stuff. You could suspend a 2x6 up there with hanging wire and setting on metal braces to moung your fan on.
It really takes a person with engueniety and creativity to look up there and conquer and overcome.
Ask around at pro shops on how this might be done in a safe and secure manner. I am sure its done all the time especially in restuarants and retail stores where this ceiling is used.