I'm sure there are some that already do.
More than a few probably have, but Reasonator isn't wanting to know if they do. He wants to know if we consider it morally ok to do so.
In any event, I propose that yes, it is. As unfortunate as it is, Atheists don't have a good reputation and it is severe enough that it can harm them on their ability to do good. If someone needs to clear their conscience of the event, they can simply start saying they've been questioning their faith and then say they gave it up (provided they aren't in an atheist friendly religion like Buddhism to begin with).
Is it lying? Yes, but unfortunately it can be necessary in today's world. If it is resulting in more good being done than if they were completely honest, it is better to do so and work on it later. Of course, like I said, this is if the politician in question isn't a religious atheist.