Do you really want to kill the guy right off the bat? Hahaha. Even taking it easy will get him super sore. So if he does bi and tri one day hard right off the bat, he may struggle or feel the need to take a day off the next day for say chest day. Once he goes through his whole cycle, he'll be out a week or so haha.
So I just think maybe easing in would be good, may be able to hit each muscle twice that way. But hey he's been in the gym before I guess he can decide, not that one of our suggestions is better than the other, just preference of the individual I guess. (Hell he may have a job that requires hard labour).