I had to come across this topic just as I was about to shut this down and get some much-needed sleep! Thanks PSA Man! LOL!!!
As a Christian and a radio professional (not a Christian Radio professional), I say why not play the song? If it fits that particular station or show, of course. Heck, some churches are buying game consoles and having Halo tournaments...why can't Christian radio up it's hip factor a little?
Will it help unbelievers listen? Maybe, maybe not, but it might help believers listen.
Before anyone gets offended (it was not meant to offend), please hear me out.
Most of the people that identify themselves as Christian have PLENTY of secular music in their collections, so if you want to play to a larger crowd and spread The Word, you really have to play to the larger crowd! If that means playing something positive-yet-secular, then so be it. The end (the message) justifies the means (playing something that will tilt a few more ears your way).
Maybe something like that needs to be dedicated to a show, where (after getting some press and word-of-mouth to promote what you are doing) you can pop on the mic and say something to the effect of "Yeah, we know _____________ isn't a Christian artist, but this is an interesting song." More than likely the larger listener base you're trying to attract will already know the song, so the station ups it's hip a little and you get some more listeners to talk to. The hardcore listener might not like it, but if you talk to them about what you are trying to accomplish, they might accept it.
Personally? I'd rather hear sermons on the AM band than Christian music on AM or FM. I love those.