i think going overdistance is a good idea. to make it easier, find a 50k trail race on a fairly easy course.
btw, i'll add kempainen to the list of runners who did overdistance runs. actually, as i type that i'm not sure if he went OVER 26 or just went up to 26 miles in training. either way, most people max out at 20-22 miles for their long run.