Ensure the visibility of the first item in a horizontal listview after prepending some items

Question

I have a horizontal list view where I detect if the user has scrolled to the leftmost or rightmost edge and prepend, or append, new list items respectively.

The code structure is like so:

class WidgetState extends State<SomeWidget> {
  // This list is prepended with some items when the user scrolls to the left edge 
  // (i.e when position.pixels = 0)
  var _list;

  // I use the scroll controller to detect if the user has hit the leftmost or rightmost edge
  // of the list and trigger the logic that updates the above list 
  var _scrollController;

  @override
  Widget build(BuildContext context) {
    ListView.separated(
      itemBuilder: (context, index)  { 
       return _list[ index ]; 
      },
      controller: _scrollController
    );
  }
}

The issue is that the new prepended items will push the old items outside of the visible view. What I would like to do is somehow preserve the scroll position such that the user still has to scroll to the left to see the now newly prepended items.

One idea I had is to use https://pub.dev/packages/scrollable_positioned_list and scroll to the index of the first old item in the list. However, I didn't want to add a whole new list implementation just for this. Is there a better way?