pivot grid default zone for fields

My need is to create the pivot grid programmatically and allow users to pivot the fields that they like. 

1) As soon as the data is bound to the pivot grid, it automatically creates some of the fields as RowPivotGrid and some as Aggregate etc. How to control this behavior? By the time _FieldCreated event is called, the field with Telerik's assumed type is already created. How can we override this behavior so that we check the field Name, Type etc and provide proper type for it?  (we tried to initialize fields by adding fields to Fields collection but they show up on the pivot grid, we are trying to control the "All Fields" in the panel)

2) Also for DateTime type of fields, Telerik automatically adds fields like "-Month", "-Week" etc - but while dragging them on to the grid, the month or week are not properly displayed and they don't have correct group interval either. 

Basically I am looking for the best place to gain access to the fields displayed in "All Fields" and setting them properly to Row/Column type so that when user drags them they only go to valid sections.

Thanks,