Stretching really isn't that crucial for a run like that. Not before you start. It's important afterwards, but what good will it do before you start? My point is that you shouldn't have tension in those muscles while you are running. I ran cross country in high school and the guys that I ran with went to the collegiate level...I chose not to. We never stretched before a run unless it was track season and we were sprinting. Unless you're doing a sprint, then it's not necessary. You should be doing a warm up which will help. I don't suppose a stretch will hurt, but it's not fixing the root problem. You might get over being sore the first few times that you run, but it's probably because your body is getting used to your bad form.