Aspirin- I can't remember at the moment if that's a way to make chemical herms, but did you know that steeping willow twigs (yup! where aspirin comes from!) in hot water and then cooling that water will give you a rooting liquid? It is not as strong as commercial chemical rooting hormone, but if you are a pure-organic grower, it is a fine option for a more natural rooting agent.
Do not worry about salicylic acid being taken up and stored in the buds. Not that I would spray aspirin on plants in flower, but it is a very very safe chemical. I am not certain why you would worry about finding it in urine either, since it's perfectly legal, and an ingredient in many painkillers, anti-inflammatories, and blood thinners.