Depending of what you’re doing now, you could try hitting the gym twice a day; for instance, if your schedule looks like:
Day one: chest/biceps
Day two: legs
Day three: off
Day four: back
Day five: shoulder/triceps
Day six/seven: off
One of the way of overreaching can be:
Day one morning: chest/biceps
Day one afternoon: legs
Day three: off
Day four morning: back
Day four afternoon: shoulder/triceps
Day five: off
Day six: repeat cycle
Here are a couple more ideas on twice a day training: http://www.tmuscle.com/free_online_article/sports_body_training_performance/double_trouble_hypertrophy
If you prefer a laid-down program, you have this one from Poliquin: http://www.tmuscle.com/free_online_article/sports_body_training_performance/the_superaccumulation_program ; if you pick it up, be shure to follow the supplementation guidelines (at least as much as you can, if not to the T).
Anything you choose, assuming you’re already eating like a horse, be aware that you’ll need to eat like TWO horses 