I have answered your support ticket with the same question and I will also post the described suggestions here, so other people can use them as well:
You could have a look at a good demo on how to use the RadTooltipManager with the RadChart here
and a demo which shows a text information and an image in the RadToolTip
You could also use a web service to make it independent of the current page (i.e. avoid the POST requests), then the following demos for setting the content of the ToolTip using a web service
and RadTooltip's Client-side API
might be helpful to you.
the Telerik team
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