I have not heard any response or solution to this as of this point in time.

For metadata organizational purposes, I am trying to add subnodes to jcr:content/metadata/ using the AEM Custom API Call module in Workfront Fusion.  I am trying to do this after loading a new asset to AEM using Workfront Fusion. For example, I'd like to add jcr:content/metadata/subnode1/subfield1jc...

I know this question is 3 years old - but has this ever been implemented?