The random number generator is seeded by a number that is assigned to each problem and each student. (You can see the seed if you edit a particular student's problem set details.) So the way this would be implemented would be set those seeds to a common value across all students, not to include additional .pl files. (My .pl file hack was just an easy way to get the effect you requested.)
Certainly it would be possible to have an option to reseed a problem or the whole set to make all students have the same seed. I wonder how much use it would get though. (I'm afraid I don't remember what your original motivation was.)
Davide
Features & Development
Turning off the Random Number Generator
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