Found this article, http://technet.microsoft.com/en-us/library/ms141704.aspx, that might help. It basically tells you how to convert data types in SSIS. SO you can convert from DT_STR to DT_BYTES. LIke this:
(DT_BYTES, 5) "GBMCU"
Hope this helps.
Jack Corbett
Consultant - Straight Path Solutions
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