We had this issue out in Ft Laurderdale FL, We had gum there that was probably 10/ 15 years old. When we got done with the first cleaning, we started to put a light coating of Love on the walks at night, and the sidewalks are now free of any shadows.
I know you are looking for a safer product to do this job, but if you just put a very light mist of love on it, it will do the job real well, plus it will get rid of any organic stains as well.