How it is possible to create a Plone configlet if you only declare your settings as registry.xml?
http://pypi.python.org/pypi/plone.app.registry only shows you how to do it if you are using schema defined settings.
I.e. how one maps p.a.z3cform Form to registry.xml?
It is not possible.
You need to have settings.py file.
Here is an example:
https://github.com/miohtama/silvuple/blob/master/silvuple/settings.py