My verbal memory is very bad, but my visual is very good. When I need to recall something, I keep a visual palette in my mind and array symbols or other objects there. I then modify the objects or symbols as I get more info.

For instance, to remember a shopping list I just place those items on the palette. Or pretty much any list.

For directions, I draw a map in my mind and label it, then drive it.

Since his matrix scores are very high, I would imagine he could learn to use this trick.