Calculated fields in TIBDataset


I need to add some calculated fields to a TIBDataset (or TIBQuery)

Important is not to add any fields from a table on design-time.
I want to execute a query like "select * from customer" on runtime and
it is important not to fix the resulting fields on design-time.
So I dont know how and when I can add my calculated fields.

Can anyone help me ?