For computer science specifically, that's unfortunately not possible because the GRE for CS was discontinued in April 2013.

That's really a shame for ambitious learners trying to achieve more with less time, wealth or pedigree.

It completely makes sense from the university's perspective, though.

No one (except a grad school) cares what you get on a GRE test. GREs aren't that different from SATs.

Even if that were true, which I don't believe, it's still highly useful. E.g. if someone passes a GRE Physics test, they may be able to enter a graduate program with an entirely unrelated undergraduate degree instead of spending 100k getting another.

You may be different, but I'd have increased confidence in someone's general comfort with mathematical problem-solving if they posted good scores on a test covering this: https://www.ets.org/gre/subject/about/content/physics/