The issue with adding such a restriction to the license is that it has to work within the domain of Copyright. Assuming The author of foo holds copyright on foo, but not to the output _generated_ by foo---it's an original work (assuming that foo doesn't output anything that its author does actually hold a copyright on).
I guess a good example would be a Madlib-style program, where it asks you questions and fills in the blanks in a story, often resulting in something highly amusing. The original story containing the blanks is copyrighted. The output of this program would then be a derivative work, because the original story has been modified.
But consider that the program took a story of your own (the data its processing) and output statistics, such as the word count, frequency of certain words, grammar errors, etc. This is not a derivative work. Similarly, if GNU Parallel is being used to process your input, its output isn't a derivative work.
With that said, you can have a separate EULA-type thing---which is _outside_ the domain of copyright---that imposes these terms. But that is incompatible with the terms of the GPL.