he'll at least have an idea of the best way to put on an academy award winning performance.
What to talk about:
He should talk a lot....A LOT.....about how ashamed he is that he has "brought reproach on Jehovah's name". He should talk about how devastated he is that he has damaged his relationship with Jehovah.
Jehovah, Jehovah, Jehovah, and his relationship with him. After the initial confession, ALL of his focus should be Jehovah.
He should also say that he has apologized to his girlfriend, her parents, his parents, and anyone else might have an idea of what took place.
Tears might help, but a lot of elders are unmoved by them - they consider them "crocodile tears".
What to avoid:
Any sort of justification ("she was the agressor", for example).
Talking about how much he would miss the friends if he were disfellowshipped, and how this act has affected or will affect him. The committee doesn't care about him - they care about "protecting the congregation" first of all. If they can "turn around" the guy, well, that's a nice little bonus, but it's not their primary concern.
The elders will probably ask if he has prayed for forgiveness. You can play that 2 ways: (1) "Oh yes, on my knees 12 times a day, crying, begging, pleading for forgiveness...it's the number one thing on my mind." ....or....(2) "I want to , but I feel so ashamed, I don't think Jehovah will hear me. Please, brothers, pray for me, I'm aching to restore my relationship with Jehovah..." Either one should be fine.
Unfortunately a lot depends on the personalities of the 3 elders selected. Some guys have a "hanging judge" mentality, while others try to be a lenient as possible except for the most extreme situations. If you get 2 or 3 pr**ks on the committee, it won't much matter what he says.
But the above hints would probably work on about 80% of the elders. If its his "first offense" and he sticks consistently to the script he will probably get a private reproof.