What if a person picked up the top open ream of contaminated paper and loaded the copy machine? Many people fan the sheets they load into the machine to prevent them sticking. He then goes to his keyboard and does his normal work and contaminates the keyboard from his hands.
It's possible, but I think the levels of contamination we are talking about on the copier sheets must have been miniscule. You can grow a culture from a single bacterium, but you have to breath in about 10,000 spores, typically, to contract an infection. If we didn't already have a good candidate for the means by which Stevens was exposed, I might go for it as an explanation, but we do: it's called the J-Lo letter. That seems like a much better candidate.