Assigning to a custom timeline clip from animation clip?

Hi,

If a custom timeline clip has animation curves in it, an internal animation clip asset is created within the timeline asset. Is there an easy way to assign animation curves from an existing animation clip into that one á la "Create from animation clip"? I did some digging through the code already and found that adding an AnimationClip member variable into the PlayableAsset makes that context menu option available, but this doesn't really help me because I don't know how to get the curves into the actual clip.

Thanks!