Rescheduling #2

This has been touched on before in threads... some people can consistently go in the morning before a race. Obviously, that's ideal. I've seen people in threads say things like "starting a few months before a big race, I train my body to go first thing in the morning."
My daily #2 usually happens in the evening, though it doesn't always happen when I'm not at my house, which can be an issue before a race. So how do you retrain your body?