There are two shots of the Jedi and Palpatine discussing Dooku. Go directly from: "This time we take him together. I was about to say that." to "He's a Sith Lord. Sith Lords are our speciality " (not the exact dialog). Just lay in some footsteps behind their dialog (to imply Dooku has walked down the stairs). When we next see Dooku ("your swords please"), it actually looks like he is walking away from the stairs, not the spot he jumped to.
It's my personal theory that Christopher Lee actually did walk down the stairs, and this was shot. However, Lucas didn't like something about it (maybe there was Dooku dialog he didn't like). So instead of reshooting the scene, he just had ILM use the gaudy CGI jump.