Thanks Eyup. The live sample led me in the right direction. What I was looking for was this:
Protected Sub radgrdTableColumns_PreRender(sender As Object, e As EventArgs)
Dim objParameterDropList As RadDropDownList = DirectCast(radgrdTableColumns.MasterTableView.GetBatchEditorContainer("Parameter_Id").Controls(1), RadDropDownList)
Dim objParameterDs As DataSet
objParameterDs = m_objDb.GetParameters()
If objParameterDs IsNot Nothing AndAlso objParameterDs.Tables IsNot Nothing Then
objParameterDropList.DataValueField = "Parameter_Id"
objParameterDropList.DataTextField = "Description"
objParameterDropList.DataSource = objParameterDs.Tables(0)
objParameterDropList.DataBind()
End If
end Sub