@Munter - not really an option for me, I'm afraid. But thanks for the suggestion. I am guessing there is no way to work with JSPM without external internet access and a github account to avoid throttling. I can try to avoid using anything that is in github.
The first issue - not having direct access to the internet from the build server - can be gotten around. I could enable that, and just live with the problem if github was down (it happens). However, the rate limiting is a big problem.