If you work in an office, get a big stack of wordy documents and leaf through them slowly as people walk by, making sure to move your eyes across the pages without actually reading.
If your office has a computer, unplug something non essential, then pretend to try and fix whatever issue you just caused by bending down and looking all around the computer.
Every once in a while, have a piece of scrap paper in hand and walk in a swift stride towards the copy machine, and if nobody is looking, pass by it and go take a long dump in the bathroom instead.