SelectItem "fetchData not defined" when not attached to a Form

I have a SelectItem, used as an EditorProperties for another FormItem, which needs to fetchData with a dynamically set Criteria.

I understand this is probably because setEditorProperties() simply uses the given argument as a template, so attempting to fetchData with the original SelectItem won't do what I want.

However, at the same time, I can't seem to find a way of retrieving the underlying editorform item. How can I get at that?