Yes this can be achieved (although not by RadChart directly) by using RadTooltip. This
demo showcases the functionality you need. Here
are some more demos of it.
Feel free to contact us if you have difficulties in implementing it, or if any other questions arise.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed