Well, it's not THAT easy. And also the cutomization is for commercial use, so posting source here isn't an option ( Of course I would do that...).
Basically I started by creating a custom WidgetTemplateSkin ( that one is used for the subwidgets ), a custom ConfigManager and WidgetManager ( to configure and load the subwidgets from the widgets config - so you get the same comfort as with the main config ).
Then I created a widget without an templateSkin and place it to the left or the right above the map ( or the map is moved to left/right). I attach to resize event, so that the container get's resized when the window resized.... I'm adding subwidgets via addChild() Flash/Flex method.