Thanks for the update. At least I know that it is possible and will await your blog post. Sitefinity has come a long way since I started developing with it in 3.2. In the latest version I love how easy it is to extend and modify the front views and add additional fields to the modules, but the user story for extending and modifying the backend content based modules UI did not get the same treatment.
Correct me if I am wrong, but from what I have figured out so far, the backend content based modules admin page is one huge monolithic user control that dynamically displays the UI based entirely from the configuration files.
What would really help in developing modules that do more than simple CRUD operations would be a sample that contained the full source code for this user control. We would then be able to modify it to suit our needs and then use the new custom control as our admin page user control for our custom modules (and possibly built in modules) without reinventing the wheel. Having the ability to inspect this code would greatly help in understanding and writing module UI definition code.
As it stands, from the provided sample code we only really have half of the picture and are forced to poke and prod around the outer boundaries until we luck into the combination of settings that magically do what we want (or more likely the case post on the forums/submit tickets asking for a solution).