I put together a small module which allows this. It initially needs to be started out of the browser but then the Chromecast directly loads the content from the server. You can try it out: https://github.com/flo80/MMM-chromecast

They already have an official node.js framework. Before anyone jumps in … what would you like to do with the module? Would you want to interact on the mirror? Or just send messages to the mirror without being able to respond?