While I agree with you 100% about 'harsh' solvents which was the question, what to use that was safe, and no one was suggesting other wise. I also agree, especially when Im up there, about walking on the roof is dumb. But the occasion does arise at some point sooner or later, you will or someone will need to.
Looked at the first picture shellbackcva59, picking that stuff off couldnt have been a lot of fun. Glad you got it. Oh after glueing the longer you can wait to get back on the roof the better. It takes several days to really cure, so will easily smush and slide. "No big ugly boots" :), Good luck