Tell your friend to do holding paractice. Have him keep his finger BEHIND the trigger with the intentions of never firing the shot. Have him hold on the target for as long as he can and then let down. This will hopefully program his mind to beleive that he is in control and can hold on the spot until he releases. After this phase, it would be good for him to blind bail, to feel the perfect shot without the added stress of aiming. I will not get into the accuracy triangle, but with these two methods, it is possible to train the mind to work differently for the proper technique.