Unity 2017.1 Timeline: How to target an audio channel to an audio mixer group?

Hi! I'm amazed by the capabilities of Unity's new Timeline but I can't figure out how to target an audio mixer group on an audio channel in Timeline. Old "Timeline Preview Manual" says that you can target a mixer group but I can't find a way to do this. (And strangely, I can't find a topic related to Timeline on the new manual???)

I hope I'm missing something, because this is an essential feature.

The only workaround I've found is, dragging an audio clip from project window to hierarchy to create a gameobject, set it's mixer group on the inspector, drag the gameobject to timeline (then it asks for a channel type), choose Audio track. Now there's an Audio Track generated in timeline. The audiosource is assigned there, but somehow without any audio clips. Drag various audio files from the project window to timeline and voila! Now every audio clip you put into that particular track will be played using the mixer group you assigned before on the first "dummy" audiosource.

This feels more like a "hack" than a solution so I'd like to know if there's any other way or if I'm missing something.

P.S: If you delete the gameobject on the hierarchy (obviously the one with the audio source, not the one with timeline) the track stays in the timeline with NO source assigned. It still plays, but loses the audio mixer group info. It just plays. Somewhere...