I remember the Cowboys had a good opportunity to attempt one years ago but they didn't bother because the coach at the time (Switzer I think, but not positive) didn't know you could attempt it even if there's no time left on the clock.
Also, the cynical nitpicker in me is going to rise up here. FYI everyone, it is a "fair catch kick," not a "free kick." It doesn't help that announcers and media usually refer to it as a free kick, or a fair catch free kick. But just so you all know, the NFL rule book even states that a fair catch kick is not a free kick.
Now you know.
It's also true that even though this play is seldom attempted, a big reason for that is coaches are all aware of it, and will tell their punters to punt it out of bounds for that very reason.