Try the Oxyclean product. I have used it sucessfully on blood, and a whole host of other stains, with success. I have never had a fade issue with it.

You would need to make a little paste out of it. And, leave it on for hours. I have left it on fabric for days (LOL, I forget sometimes).

Good luck! And, try using tissues instead of seat belts to halt nose bleeds. Much better absorbancy I would think.