The RTPPusher module can broadcast to a multicast IP: RTPPusher: package for pushing RTP/MPEG-TS unicast and multicast streams out of Wowza
But, you can not use multicast over the Internet.
You can use a CDN (Content Delivery Network) service so that the only bandwidth you use on your network is to send the stream to the CDN.
There is a concept called “P2P streaming” that is designed to reduce client-server bandwidth.
But, for the most part, the only way to reduce bandwidth is to reduce stream bitrate.