It depends on what the nature of your program is.
If, among other things, your programmer inserts extensive pre-processor macros, then changing that behaviour may be impossible. Also note that if person A creates a document, B modifies it, then C makes modifications that (among other things) remove everything that B did - B still has copyright on the final result! (Copyright is a funny beast.)
Also note that if you try to implement a ton of restrictions beyond the simple approach that I just described, you will run afoul of the fact that your license is not even remotely compatible with the GPL. This is a Bad Idea.
For further discussion I suggest signing up for fsl-discuss. They are much better equipped to give you feedback than random Perl hackers. | 
