I'm not sure what I can offer. I think what you want to do makes sense for many non-trivial uses of GoXam.
As it so happens, each of the separate samples within the GoWpfDemo application is implemented as a UserControl. Now there does not happen to be any additional API that is added to each such control, either to implement some interfaces or by inheriting from some particular class derived from UserControl, but that is probably what you want to do.
I suggest that you search the web about defining your own UserControls.