User Community Feedback

I often need to share my screen via WebEx meetings and give clients ability to control my desktop so that I can gather user feedback and observe any issues they may have in using the interface. This is done as a 1x1 interaction, however often I have multiple silent observers on the line as well. I need the ability (which I had in an older version of WebEx) to suppress the list of participants AND video thumbnails for all participants, so that the client whose feedback I am gathering does not know that there are multiple people watching them. It helps them to feel more comfortable and therefore behave more naturally. Right now I can suppress the participant list but NOT the video thumbnails. Therefore the client sees how many other people are watching.