Enumerating Audio Sessions for All Users

I'm trying to control the sound mixer of a different user on my Windows 7 machine. I have administrator privileges, and I want to mute some annoying apps because they still can play sound even after switching to another user. I can't kill the process directly because there may be some important information.

So far, using WASAPI, I have retrieved information about current user's mixer. Is there a way to do that for every other user on the same machine?

Another way of doing this - have an instance of my program for each user and communicate with them over sockets or something. But it looks way too complicated.