alt Hacker NewsDoing this in a way that doesn't get you noticed or fucked with is potentially going to be quite difficult.
If they have a "hey we're being benchmarked" mode, which is not hard to imagine, avoiding tripping it is going to be annoying and difficult to prove.
You would want to use your own benchmark, certainly, not something publicly known. But outside of that I don't think "this is a benchmark" is such an easy category to determine -- a benchmark should be similar to a typical scenario anyway.