Just some updates~~~
He hasn't hissed at me since I wrote the original post. :) Even when he runs to hide from a stranger or noise, I can still go right to him and scoop him out of his spot with no resistance. He's finally started to associate me with food and treats and is not afraid to come...
About 7 weeks ago, a family of five newborn kittens and presumably the mother cat were discovered in a semi-enclosed area outside at my job. I work overnight at a place that stocks and sells hard-surface flooring in bulk, so there are forklifts, reach trucks, pallet jacks, etc running constantly...