I've told close friends who won't be offended - including agnostics and atheists - that I've prayed for them during rough times. They always seem touched, however much they question religion.

What makes it touching is that you know he believes - even if you don't - and that this is a sign you have some importance to him. I don't think it's necessarily chameleonness. It's not like you're learning about football so you have something to discuss with him.