You can add a level of interactivity to your webcast presentation by letting your audience members wave. For example if they are working together on an exercise and they need help, you can ask them to agree to waive to the webcam.
Also when you get a question from one of the members of the audience and you are not certain if the question is very specific and only relevant for one person you can ask the other participants to the webcast to waive in front of the camera if they are also curious about the answer. If not, then you would follow-up with the individual alone after the webcast to address the question. If you see a group of people waive for the camera you can answer the question for the entire group. Using waive elements to your webcast presentation will add an interesting way of interaction with your audience.