There seems to be no way to find a working solution to that so maybe it's an option for you to use HTML 5 drag and drop instead. E.g. https://github.com/StackHive/DragDropInterface. As I have the same issue I will probably go into this direction.
Edit: There is a more advanced library. See this answer: Offset issues with jQuery Draggable into an iFrame based SortableOffset issues with jQuery Draggable into an iFrame based Sortable