You may also want to try a rhyme or acronym, to help him or her remember basic metric units of measurement: Kilo Hecto Deca Unit Deci Centi Milli (KHDUDCM). From there, you can either make up an acronym, with a word starting with each letter of the units of measure, or use one that's tried-and-true-- like "King Henry Doesn't Usually Drink Chocolate Milk."
Lastly, the final link: a "Make Your Own Ruler" activity, might be helpful, too. You could try this activity using metric measurements. Perhaps, going through the process of building a ruler of his own will bring the concept of increments of metric measurements home for him.