I have had to do this to an extent. I found it nearly impossible for me to pull it off because of the strong feelings I have about the evils of religion and the religious mindset. Having experienced a lot of early bullying and discrimination my view of religion is similar to the way a Jew would view Nazism. Most of you guys are younger and didn't have to live through that sort of thing, so you might be able to pull it off.
A more important question in my mind is why you think this "friend" of yours is a friend? He essentially sees you as being on the same level as a child molester--while at the same time has no problem with indoctrinating children to believe ridiculous fantasies.
It would be to difficult for me to do it, especially if it involved kids. It's one thing to know they indoctrinate these kids at a young age but another to witness it; pretend to enjoy it right along with them. Impossible, I could last maybe a week before I would blow up over it.
As for your friends comment - 'corrupt children' I would have died laughing right there on the spot. Who would ever want children to think for themselves, have individuality and see the world as something scientifically beautiful. *eye rolls* Damned Atheists and their corruption of helpless children.