This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Not modify the source? Can you call/start the program in question from another program? If so, in the calling program you can change the value of System.out (setOut()) to be a NOP method before calling the program you can't modify.