He could upload it on bitfinex and use the free MarginBot to lend the USD out to traders. He would receive around 20% a year. At least it was that way some months ago.

The risk would be that bitfinex is an exchange and exchanges can go down.

Investments are always risky. You should think of them the way that you might get 100% in a year on top of your investment but when you start you lose 100% and the question is open if you will get your investment back at all.