SQL 2012 :: SSIS Data Flow With Case Statements

I would like to know how I can add the following sample code to my Source data on Data Flow on SSIS, or what other options there are. The main issue is time as we have talking about 100's of millions of rows

select Sample,
CASE
WHEN Sample IS NULL
THEN NULL
WHEN SUBSTRING(Sample, 1, 6) IS NULL
THEN ' '
ELSE RTRIM(SUBSTRING(Sample, 1, 6))
END AS [Sample_1_6]
from TestTable

what I have done at this stage is just to Create a SQL task with a Insert into

INSERT INTO [dbo].[TestTable1]
([Sample]
,[Sample_1_6])
select Sample,
CASE WHEN Sample IS NULL =THEN NULL
WHEN SUBSTRING(Sample, 1, 6) IS NULL THEN ' '
ELSE RTRIM(SUBSTRING(Sample, 1, 6))
END AS [Sample_1_6]
from TestTable

If there is a way adding this to a dataflow so I van use fast load that would really be the best solution. I know there are derived columns, but would this really be faster than the straight insert into in a SQL Task? If this is the way to go what is the code I would use in the derived column or any other option.