Do you have a webcam? If so, most models have a 5 second delay feature. If yours doesn't, then try my poor mans method.
Now this sounds nuts, but postition the arrow over the click to take pic part, then carefully put the mouse on the floor. Pose, and click the button with your foot. It's tricky, but I used to do this before I got a better cam. It was the only way I could take full body and back shots.