Unfortunately such a requirements goes far beyond RadGridView's core concepts. Basically, RadGridView is designed to process all of the column cells' values as instances of a same type. You can have strings, numerics etc simultaneously as they all derive from System.Object, but this will disable all of the data-shaping operations (sorting, grouping etc). You will also need some custom type-casting mechanism. I would personally try RadSpreadSheet instead.
the Telerik team