ScrollView include elements that aren't children

[JobRecrd]

I need to include a rectangle in the scrollbar area, I can drag it from the header to the content of the page, then this will work, but I need this rectangle exactly in the header(I need this rectangle on several pages).

ApplicationWindow {
    id: appwindowwindow
    width: 800
    height: 600
    header: Item
    {
      id: item
      width: appwindow.width
      Rectangle  {
               id: myRec
               width: 300
               height: 200
               radius: 2
       }             
    }
      ScrollView {
              id: scroll
              ScrollBar.vertical.policy: ScrollBar.AlwaysOn
              ScrollBar.horizontal.policy: ScrollBar.AlwaysOff
              ScrollBar.vertical.interactive: true
       Page
      {
            id: firstPage
            ColumnLayout  {
                          //there are many objects     
         }
    
       }
    }
}