Compilation makes it difficult to include this kind of useless detail in software, you'd have to do some demonstrably pointless task that survives the compiler somehow like filling an array with a specific sequence of hardcoded numbers

You could have dead code that the compiler cannot recognize as dead and therefore cannot optimize away (basically everything the type system cannot catch). For example, given a function(int x) where, to make sense, x can only be an even number that is a multiple of 42. You are free to handle all x that don't match the criteria however you want, though you'll burden yourself with bad error handling should an invalid x slip through at the caller's site.

Much easier (and safer) would be to find n characters or words in strings which, when replaced with another one, don't change the program's behavior or misguide the user - documentation, menu labels, error messages and so on. This way you can even include a n-bit identifier to identify the copyright violator.