Have you tried the memory palace technique? I wonder if you could put the moves into a memory palace and then recall them that way. To create mnemonic images for the moves, imagine a motivation for each move. Example: reaching above head = picking an apple. You could turn the moves into a story.
Tai Chi already has names for the exercises. Like rising/setting sun. If you write these in the standard order in which they are normally done, you can memorize those words in the way Josh has described. I don’t know the names offhand but, something like Rising Sun, Setting Sun, Tea pot, Crane. Sorry about the tea-pot but, I don’t recall the proper name ironically but, I do remember calling it that when I was a kid.
He will have to anyway Graham. That’s what they do in the classes. They always start at the same position and always go through the moves in the same order.
I think this is were spaced repetition can come in quite handy. Learn the first five moves, then brake for 10 minutes or so then go back and see if you can still perform them. If you can then start with the next five, but time off 30 minutes, at which point you will go back and review the first five and so on.
Also I think using the memory palace could be very useful, because there is nothing worse then practicing by your self a new form and then forgetting a move with no one around to remind you that it is. And the techniques in most Chinese martial arts have colorful names which lend themselves very easily to memory techniques.