SSIS Expressions Date Format get just YY for year
Use the modulo operator %: http://technet.microsoft.com/en-us/library/ms141815(v=sql.100).aspx

DATEPART("yyyy",GETDATE()) % 100


Your next problem may be that this will still be be a number and thus will not have leading zeros.

What is your underlying problem?  What are you trying to format a date as?

You would then just use (DT_WSTR, 2) DATEPART( "YY", GETDATE()) % 100 as part of your expression.