P1 while traveling could be difficult, but if he really wants to work it out he can. Eggs for breakfast with a glass of tomato juice. Chili and a side salad for lunch. Bun-less burger and veggies for dinner. Etc... Snacks are very important in P1 to keep your blood sugar stabilized, and that could be the most difficult part for him.
Him being a week behind you in P2 isn't going to be a big deal at all. When you enter P2, you gradually add back in your fruits and starches 1 week at a time, to see how your body will adjust. It can be a good 6-8 weeks to fully transition into a P2 with up to 3 fruits and 3 starches a day. That 1st week when he is back, you would/could be adding something as small and simple an apple into your daily foods, and he just won't be having that apple. Does that make sense?
I'm a big proponent of not staying on P1 any longer than the recommended 2 weeks. P1 is there to kick your sugar/carb cravings. P2 is your path to weight loss and a life-long change in the way you eat. The weight loss that happens in P1 is primarily water-weight. P2 is where that stubborn fat starts melting away!