I disagree with the original poster’s premise. In our times, negative reinforcement as a policy can only be detrimental. Not only would it NOT instill yiras shomayim into slipping individuals, but it would probably further their disillusion with Yiddishkeit. Showing them concepts of punishment that are not concretely applicable to them has no practical purpose.
I don’t think that the motivation in most cases is lack of fear. The thought of gehennom is not what inspires ME not to sin – it’s my conviction in what is right that does. There are so many mixed messages being given to our youth that only the strongest can claim such conviction. I think that if people try help the confused BEFORE their confusion precludes their belief in Yiddishkeit, there really would be little need for negative reinforcement. Wouldn’t that be ideal?
Tthen again, this idea may be as practical to implement as the OP’s is. I don’t know. But a little love and understanding goes a long way.