I've never intentionally added something that I used as a distraction from the rest of the work, but I have added requested features--that I thought were poor design--in a way that would be very easy to remove. Later, when the client finally agrees that it is a bad feature, it's no trouble to remove it.

I've also just hidden things that the client has asked removed if I thought they would eventually ask for it again, once they got to using the software. They usually do, and they think I'm a "genius" when I can make these "big" changes in such short periods of time.

Hell, I even tell them I'm going to do it. I'm always very forthright with my clients. But they never remember. They always think I do everything from scratch. I guess because their own developers do, they think we all work the same way.