Just keep up with the pack, and when you get close to the finish line, get off your bike and snipe all their heads off. You just have to watch your timer, so you don't fail for being off your bike too long. If necessary, get back on your bike, get back off, and finish shooting everybody. If you're the only living person in the race, as soon as you cross the finish line, you win. It does work, and I wish I had known about it my first time through.