I see that you are disturbed that your patient regularly attends church, but allow me to quell your fears. Church attendance is not as threatening to our cause as one might think it is. Our Father has no qualms about people who attend church, so while I would advise you to prevent him from going if possible, do not allow Sunday mornings to cause yourself much worry. If he walks into a church, hears the droning on of a pastor, and walks out with minimal interaction with other people, you have nothing to fear. Better yet, he even thinks that he is doing what is "right." Our enemy does not keep a tally of people's church attendance, but it is best that we keep them unaware of that fact.
It is, however, your responsibility to prevent any sort of engagement between him and the other people in attendance. Our enemy knows as well as we that there is nothing more powerful than a united force, yet we have worked extensively to prevent modern churches from becoming such forces. In fact, the humans' lack of awareness of the distinction between church attendance and church involvement was accomplished by our fellow tempters at the Anti-Faith Based Commission on Churches. Together, we have successfully convinced many humans that they are doing well to simply attend Sunday morning services, which has greatly prevented our enemy's desired work within his altogether foolish notion of church.
You must do what you can to convince your patient that he does not need to do anything more than attend church. We run into trouble when they start to get engaged and involved with each other, so it's best to keep up strong and unseen barriers between the pews. Make your patient intensely aware of the quality of people surrounding him in church, and convince him that such people are beneath him. You yourself write that he has grown up going to church his whole life. There are few things better for our cause than people who consider themselves church connoisseurs. Create in him a desire to critique the church's program, for a judgmental attitude will completely distract him from any of the enemy's words he might hear. Bring attention to lengthy announcements, music that is off-key, lyrics that are missed, an overuse of smoke machines, and awkward transitions between songs. All these things, despite their trivial nature, can completely derail a church service for your patient, and if he loses interest even before the preacher is on stage, you have done well for yourself.
If your patient remains interested amid the distractions, remind him that he is simply there to hear an excellent public speaker. Have him focus on the illustrations and mannerisms that the teacher uses as opposed to the actual content. The humans will consistently flock to hear their favorite teachers, and as long as they are focused on quality of speaker and not quality of content, we are winning. Preachers that are excellent teachers can be equally useful to our cause as those that are terrible teacher. Regardless of which type he hears, have him focus on how the words are said and not what the words actually mean.The truth is, and this is not something I readily admit, but humans find the teaching of our enemy irresistible. We would do well to keep his words from their ears, and we must confuse the words that they do hear.
You must know that Sundays are our busiest workdays. Even after you have done everything you can to minimize the impact of church, some of your best work can be done on Sunday afternoons and evenings. To start, it is imperative that you keep his mind focused on the negative aspects of the service he just sat through as he's on his way to lunch. You should already have him making lunch plans while the pastor is not yet halfway through his talk, but it is also important to keep lunch conversation focused on anything but church. Ideally, you want your patient to walk straight out of church having completely forgotten what he just heard. However, his memory of a teaching can be improved if he is encouraged to discuss its content. Do not allow for discussion. Distract him and his friends with sports and the upcoming work week, and prevent them from sharing what they "learned" at church. I assume that you are already in communication with your associate tempters responsible for his friends. Work together and keep the conversation of your patients far from matters pertaining to our enemy.
I must add that Sunday evenings provide great opportunity for temptation. No doubt your patient is tired from a busy weekend and discouraged at the prospect of going to work in the morning. Humans are weakest when they are tired and when they are upset, and you will find that Sunday evening often provides both of these emotions. I expect even a demon as inexperienced as yourself knows how to take advantage of such weakness.
You are young, but you are beginning to show promise. Pay attention to every word I say, heed my advice, and you may create an expert sinner for yourself just yet.
Your selfish guide,