If you have an account yourself, I believe your son could transfer the miles to you. Otherwise, you could use the miles to buy things from the Lufthansa Skyshop (I think that's what it's called).

Or, your son could somehow "sign up" two new members and thereby earn another 1,000 miles. If you book a so-called "Flysmart" award online, intra-european tickets go already for 17,000 miles which is a very good value, I think (however, you don't live in Europe, so this might be of little value to you).

Or, if you wish to exchange the miles for something else, you could try your luck in the Flyertalk "coupon connection".