I agree with your findings, DDP RPC is a way for the client to call arbitrary methods on a server, but there's no RPC facility from the server to the client.
A Meteor publication should do what you want, though. You can use the low-level added
/changed
/removed
interface to send arbitrary data to subscribed clients whenever for whatever reason. You probably only have to implement, say added
. Let's assume you do this.
The client can do whatever it wants with these data. It just needs to call sub
, then it will start receiving your added
messages.
This code might be a decent starting point. Again, if you only ever send and look for added
, you only need to implement that one bit on the server and client.