Unfortunately, you can't. In my opinion, people (and I'm talking in a broad spectrum generalization that in no way singles out a specific person) are stupid. Other people will make choices that to you personal viewpoint are logical, but to them may be sound. So, no, you can't stop him from making choices that (from your point of view) are stupid.
As for your argument, I'm speaking from the openly admitted viewpoint as a future petroleum geologist, so my logic train is clearly biased. That being said, the fact is electric cars are very inefficient. They get at most ~250 miles of range, they're incredibly expensive when compared to the same automobile using a fossil-fueled powered engine, and the infrastructure necessary to maintain/charge them doesn't exist in the same way that there is for a fossil-fuel powered car. In addition, the source of energy needed to charge them (which, for the most part, comes from fossil-fuel burning power plants) almost completely negates the "Green" aspect which is what I'm assuming is why he bought the cars in the first place.
If he's really looking for moderately clean, proven, safe, and no fuss way of getting from point A to point B, point him at a diesel car. They're cheap, they get great gas mileage, and you can find diesel stations all over the place.