How to download an animation from my server, and add it to my avatar on mobile device?

I am building a mobile app. I want users to be able to download new animations every week for their avatar.

The legacy animation system has AddClip(). Since MecAnim doesn't have that, how can I download a new animation and add it to my avatar's MecAnim?

For adding a 3d asset, I can use WWW to download the asset bundle, and then call AssetBundle.Load() and Instantiate(). How do I do the equivalent for a MecAnim animation?

Thank you!