Create proto schema at Runtime?

I have been using protobuf.net for some time with its IExtensible feature (allows me to create runtime proto message-streams). Unfortunately, there doesn't seem to be any functionality to extract a proto schema from an Extensible class. I need this functionality so that its a little easier to get protobuf.js to read the message stream.

Is there a way to generate a proto schema for a Extensible/dynamic class?