You can, however you need to use Event Center to do this, you cannot do this in your personal meeting room.
With Event Center, you may invite panelists when you schedule the event, or promote an attendee to a panelist within the event. For more information about what a panelist is, what they can do, and how to add or remove panelist privileges see the WebEx knowledge-base answer here.
The host can enable video sharing for up to five panelists.
To allow panelists to share video:
1. Enter full-screen mode.
2. Click Panelist Video Options in the upper right corner of the screen. The Panelist Video Options dialog appears.
3. Click Allow to Send Video, the select check boxes for panelists you want to allow to send video.
4. Click OK. Up to five thumbnail images can be displayed in the Participants panel.