I was having some issues getting SSEs to work on a local Particle cloud, and after adapting from the example posted by @krvarma over here, I’ve been able to get a locally-installed freeboard and Particle cloud (spark-server) going.
Code and instructions: http://chuank.github.io/freeboard-plugin-particle-cloud/
The same caveats exist for local clouds not being able to publish device-specific events, so you’re limited to the event-specific firehose. I’ve written some basic instructions on the github page to describe this.
Many thanks to @krvarma, for the original work on his freeboard SSE plugin.
[EDIT: updated url for code repository]