CDN integration with WordPress Multi-User

We are trying to integrate Rackspace's CDN with our multi-user setup. The process is pretty seamless until we throw the multi-user "monkey wrench" in the mix...

Here are the questions that Rackspace wanted me to ask in regards to multi-user...

1) Is there a plugin or feature to enable CDN for media assets in WPMU? Do you have specific instructions for Rackspace CDN or any other CDNs?

2) Can this be turned on for only one domain at a time? Will it affect the other domains?

We use domain mapping and WordFence.

As always... thanks....