If he really wanted to, he would just have to wait until brick-and-mortar stores or online stores accept BTC as a form of payment and he could spend those BTC directly there, no need for selling them first.
There are already many stores online and in the real world where he could spend his coins.
Regardless of that though people would go crazy as soon as the coins moved anywhere and would spend a lot of time trying to trace them. They then likely would be able to be traced to the stores he used them at.
If the coins is moved then expect bitcointalk is gonna be a mess since people will thought that satoshi is coming back here and the price might have a short rally . If he used it to buy at a stores or cash them out , the anonimity of satoshi will be reveal since it can be very easy to track on