Retention of the basics is the main go/no-go part of deciding whether one should become a pilot. If he can't retain engine-out procedures at the pace of an average human being, then flying is not for him. While you might feel like it is not "your place" to crush his dream, you are probably saving his life. We do not need more of this type of person putting our industry in the public view with an accident. Or flying into the Washington TFR and giving another reason for them to ban GA for a 100-mile radius. Even if you get him to proficiency, you have no means whatsoever to ascertain if he will retain the skills for the period beginning after his checkride. What about 12 months down the road when he has had no dual since? That is why retention is more important than everything else. Without retention, he will turn into a low-time student whenever he gets 'stale', without someone else spoon-feeding him.
I have noticed that many brilliant people make substandard pilots. They are creative, easily distracted, and easily bored. They often like to mull over problems and look for perfect solutions, rather than jsut get the job done. Flying is not for everyone, no matter what they like to say in the magazines.
Do this man a huge favor and politely tell him that he should focus his efforts elsewhere. You are probably saving lives if you do so.