Dont think it is the end of the world though. I suggest to use a little trick to display your cursors on the chart:
1. Create your chart as normal
2. Create a graph, then create cursors as normal.
3. Use the color tool to make the Graph border and its grids to transparent color.
4. Untick all the visible items for X scale and Y scale, so that you only see the cursors.
5. Move the transparent graph on top of the chart, adjust the cursors to your desired positions.
6. Enjoy watching the chart updating with the fixed cursors.
Hope this is what you are after.
Pics attached to demonstrate the idea.