Are you sure you need them? Judging by the fact that you're using a day dedicated to the repetition method rather than the dynamic method suggests you're not an advanced lifter.
Remember, one of the corner stones of westside lifting is have 72 hours of recovery time between workouts. Also, the point of using a split like this is to maximize performance in each workout. Guys like Louie and Chuck do close to 14 workouts a week, but they spent a long time working up to that work capacity.
If anything, I would place the extra workouts the same day as your upper body days, later in the day. The boosters are a good type of recovery workout, but I would choose one muscle you're looking to work specifically (generally for westside, triceps or hamstrings) and one muscle you're looking to speed recovery for. Also for recovery movements, try to find things without an eccentric phase (sled work, medicine balls, etc.).
When Bob Youngs first went to westside (with a 1450 total), Louie had him do only 3 exercises per day. The trick is to achieve the proper volume for the main exercises. Go to the elite fitness webpage (Dave Tate's webpage) and read Jim Wendler's beginner mistakes articles.
I'm not trying to say that extra workouts are bad, but the 1st lift on your ME day, and the first lifts on your Repetition method day will account for an overwhelming portion of your gains, so do anything you can to support these days.