You can save your stripped mainwindow as a template to load (File menu -> "Save Form as Template...").

As for stripping the other widgets you can try to edit the ui file manualy, it is xml and fairly readable. Or, if you have the template you want on windows, maybe try to copy that over to your templates folder on linux.

Also, if you are not using the functionality provided by the mainwindow class, perhaps you should use QDialog or even a QWidget as the effective main window for your app.