Hi there!
You're on the right track. You will need to proxy the call to the analysis URL somehow. If Yahoo is being sketchy for you, you can find another proxy service, or make your own.
We have a repository for setting up your own remix server, which both handles the proxy call and caches audio uploaded by the user: https://github.com/echonest/remix-server. That might be overload, though - simpler might be to make your own proxy call on your server.
Hope that helps!
Thor