Since you'll have the x,y positions for the chart anyway could this not be done with an external mouse over object? Something like an image map if that makes sense.
If it's mousing over to get the value, since I'm not intercepting windows messages yet, it's possible using standard DesktopX callbacks.
For axes names, ticks and legends, you really want to be able to draw text. Using DesktopX objects to achieve that would be kind of tedious, especially if the graph is built dynamically.