How to group actions in a context menu?

[pabrams]

This describes how to add an action to the work item context menu. I've added four actions, now I want to group them in a parent fly-out menu, like the out-of-box "Templates" or "Add to Dashboard" menu groups. How can I accomplish that? What contribution type do I use?

[pabrams]

I found an example (Edit: I had the wrong URL) that shows how to do it when the menu values are dynamically assigned. My values are static. Is there a way to add the sub-menu actions via vss-extension.json, or is the above javascript solution currently the only way?