You can achieve your requirement using the approach with the trackball from the Zooming and Scrolling example along with custom LabelDefinition for the series. Basically, you can show the labels of the series, then define a property in the data points view model that tells if a point's label should be visible. After, this you can define a Template for the custom label definition and bind the Visibility of the element int he template to the property in the view model. You can use the TrackInfoUpdated event of the trackball behavior to get the highlighted data points and set the property that determines the visibility of the label.
For your convenience I attached a sample project demonstrating this approach. Please give it a try and let me know if you need any further assistance.
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items