No rush, I only doubled my reply because I re-read my initial one and realized that it was a very poor answer to your question 
You'll have to excuse my excitement though; this wasn't a feature that I had in mind when I wrote the system, and it makes the extra effort I put into the yaml file layout seem much more worth it. As much as I'm interested in whether it works for you, I'm also interested in knowing all the steps you have to take in order to make it work.
My thinking is that it might be possible for me to add a config entry to the YAML file that would let you specify a path on disk (or some other locator) for a still-in-development hardware package. Then it's just a question of how to act on that information (e.g. forcibly copying it into the Arduino IDE each time, in case changes were made to it). I just need to learn more about the development cycle for hardware packages.