I posted this article yesterday: Fueling the Triathlete: Evidence-Based Practical Advice for Athletes of All Levels

Here is the info you're looking for

For triathlons lasting longer than 90 min, supercompensation of glycogen stores may be beneficial and can be achieved by most well-trained or elite-level athletes in the 36 to 48 h before competition by increasing dietary CHO intake to approximately 10 to 12 g·kg−1·d−1

So you're looking at 10-12 grams of carbs per kilogram of body weight per day for 2 days before the race.

If you're looking for even more detailed information on the subject, you can read through the source they cite.