The functionality you are looking for cannot currently be achieved. It requires a mechanism for setting dependencies between fields.
Grouping by more than one field will be introduced in one of our future releases:
"CustomerID, CustomerName Group by CustomerName DESC, CustomerID"
This expression currently generates two grouping levels (one for CustomerName and one sub-level for CustomerID). This, however will change to a single level of grouping, where CustomerName and CustomerID will be the same, and sorting will be done on CustomerName, then by CustomerID.
If you have any additional questions, please contact me.
the Telerik team