I've not done the race, but went up there one night with a guy who has done it a lot. We crossed to the right hand bank of the stream (as you go up) and basically headed up, trending right slightly, but picked up faint tracks, and then joined the ridge near the top, fairly much in a straight line, slightly veering rightwards. It was suprisingly runnable, although we'd only come around from Capel Curig.