I did this one using the Splash Down Danger Sign, all you need to do is back up a little ways on the road after you fast travel as close to the Danger Sign as you can. When you go off the ramp, make sure you go off of it at a left-ward facing angle, trying to go straight ahead will put you in a ravine on your face. Going left off the ramp will make it a very short jump but you're almost guaranteed to land it on your first try!