As for now there is no built-in way to achieve this. The only possible way is to edit the template of the control and put a tooltip to the header with the desired value. Let us know if there are any further questions.
the Telerik team
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? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items