I would get middle eastern Christians involved in vetting Christian refugees. They know the quirks and tells of muslims trying to pass themselves off as Christian.
You're absolutely right. It's also a task that wouldn't slow down Israeli intelligence at all. They could tell us some tricks. (Just don't tell 0bama's people.)
And if the test produced some false positives, they can go to the back of the line and try again. Better safe than dead, thanks.