I am afraid RadChart does not provide such type of grouping. Each chart series item can get the values for the corresponding XValue and YValue properties from the underlying data. It can also group the items in series, but still, the XValue will be respected (or if no XValue is set -- the items will be added consecutively).
However, you can manually alter the chart after it has been databound in order to achieve the desired result. I have attached a small page showing this.
the Telerik team