FormFieldFactory - How to get components to interact?

I have a simple use case: I have a factory that has two combo boxes, the first (when selected) determines what is filled in the second.

I’m trying to figure out how to get access to the “other” combo instance to populate the data.

I’ve tried adding a listener, which works well enough, but gets the original value of the bean item, not the current one.

Does anyone have any tips? The only thing that occurs to me is a rather inelegant listener on the first combo to write a value somewhere, so the second combo can fill itself.

This seems to be a duplicate of https://vaadin.com/forum#!/thread/458749