playing music through line out for chat rooms

I participate in several on-line chat rooms that are multi-user camera chat. One example is camfrog. Another one is Paltalk.

How can I set the Macbook air to play directly from the computer to the internet chat room, WITHOUT using the microphone and speakers? Effectively, this would be streaming music to the chatroom.

On a PC, one has the option of setting up the sound card to play through a line out (as well as the speakers) and the line out replaces the Microphpne in the settings. This will play any sound your sound card is playing, including movie sounds, music, or a podcast - any time the mic button is selected in a chat room.

Can it be done? How?