A checkbox is displayed on every block defined as selectable. By checking this box, the visitor creates a selection he can see and modify in a display selection component.
Make desired blocks selectable, anywhere in the site.
Add a display selection component, in any page of the site. This component will display all blocks selected by the visitor.
Note: that selection is stored in a cookie in the visitor's station, for one month.
Select the selectable block then reload the page.