P.O.
A.,
How fun! I'm sure that there are lots of folks that were in drama that could help you, but I know one suggestion I followed when I was kid was to review what I wanted to memorize right before I went to sleep at night. My grandmother had read something about how you can set memory better by reading something right before sleep and so that's what I did. Sounds like he has a lot to memorize, so I wouldn't review everything every night right before bed, but I would take 1 or 2 things to go over just before bed (in addition to the practice during the day). Worked for me. In fact, many of the poems that I memorized this way for recitation as a child, I can still repeat.
Good Luck to him!
P.