Whats the best substitute of Coca Cola Pepsi for an addict?

My friend's father is an addict of coca cola/pepsi. He has been suffering with chronic diabetes for last 12 years and has been going dialysis everyday. Even then he doesnt stop drinking coca cola. We tried to talk to him, take him to practitioners etc etc, but he never listens to us and uses his power and... show more My friend's father is an addict of coca cola/pepsi. He has been suffering with chronic diabetes for last 12 years and has been going dialysis everyday. Even then he doesnt stop drinking coca cola. We tried to talk to him, take him to practitioners etc etc, but he never listens to us and uses his power and authority to get himself one everyday. We want to know if there is any substitute for Coca Cola that makes him feel the same but is less dangerous? Like one which looks the same and tastes the same, so that he doesnt know he is drinking something else. How about Diet Coke, Coke Zero? Are they worth a try?
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