Is it possible to use an avatar mask with the new AnimationClipPlayable et al.?

Hi

I have a complex animation requirement.

Specifically, I will need to make hundreds of animations built from smaller modular parts recombined in different ways - if I make the graph by hand there will be 3 graphs containing around 500 nodes each.

Originally I intended to use a StateMachineBehaviour derived type to play specific sequences of animations in each of a smaller (but still approaching 100) number of states in each state machine.

It appears that this isn't possible (!!!) & it looks like I might need to use the new Experimental.Director animation stuff to accomplish it.

However, based purely on having read the documentation so far, there doesn't seem to be any way to control which parts of an animated object that AnimationMixerPlayable updates on the Animator that is playing it - which would normally be accomplished by use of AvatarMasks on the layers of an AnimatorController.

I've looked at the HumanPoseHandler which uses Avatar objects to apply a pose from one transform hierarchy to another but this also doesn't seem to support the use of AvatarMask objects to control which parts of the object are updated.

In an ideal world I'd like to be able to play AnimationClipPlayable objects on a specific layer of a regular mechanim graph from within a StateMachineBehaviour derived type.

I've watched the whole of this "Unite 2015 - Leveraging Unity 5.2's Advanced Animation Features" from Unite Boston 2015 and it doesn't offer an answer :(

https://www.youtube.com/watch?v=HOURak6BpSo

Any or all help in how to do this is much appreciated...

My only other option seems to be to have a system that generates multilayer AnimatorController state machines from some sort of data file outside the editor; which I really don't want to do unless I have to...

Alex