First webRTC project, what is the best network topology for single source broadcast with low processing demands for the source?

This is my first project that involves networking, and webRTC interests me in how it allows for peer to peer connections without the need for a central server. I'd like to make a simple mobile application that allows a single person to live broadcast audio to a large group of peers. So some sort of one to many connection? I'd like it to be scalable to more than 256 peers, serverless (strictly p2p), and since it's mobile oriented, have a minimal load on the broadcaster. This would rule out a full mesh network because it connects every peer to each other, and I believe it also rules out a star topology because that still has the source connecting to every listener, and I can't imagine that scaling to large numbers (300+). What I'm picturing is something similar to torrents where you connect to some peers, but not all, and not necessarily the initial seed. However, I'm not sure this is an analogy that can be applied to the webRTC protocol. Here is a picture of what I have in mind... http://i.imgur.com/gtC1ah8.png

This is my first week looking deeply into networking so I apologize if I used terms incorrectly. Any guidance or direction towards resources to read would be greatly appreciated. Everything I've been able to find seems to revolve around connecting ALL nodes to each other or using some sort of MCU server to handle the load of connecting all the listeners.