Populating Combo Field with OPal?

How can I populate a combo field with only a subset of a table?

If I use the DataSource property (as in self.DataSource = "[tablename.fieldname]")  the list is populated with all entries in the table, but I only want a subset of them.

I tried using a TCursor to filter the table, but I can't find how to manipulate the list. The code I tried is as follows, RecTC is the TCursor which has a range limited to those records I need, I the try:

   i = 1

   RecTC.Home()

   Scan RecTC :

      Prestador.PrestList.List.count = i

; Up to here it works, and I get a Combo list with blank fields, but then neither of the following work to set the value of the fields:

      Prestador.PrestList.SetProperty("List.Value",RecTC.Recurso)

      Prestador.AddString(RecTC.Recurso)

      i = i + 1

   endScan