If you really care about your friend better to tell him everything, and teach them how to play in the market. Im not saying that you idea is illegal, its legal as long as you are committed but again teaching him about cryptocurrency is the best thing that you can do, let him enjoy the cryptomarket.
I agree with you. Teaching him the ways to cryptocurrency will be beneficial for it because another member is added into that field, not to mention that his friend will, later on, introduce it to another friend. It is like advertising. Moreover, it is better that he does it by himself because if something goes on the wrong foot, he will blame you for it. It is better to avoid taking risks even though I believe there will be no risk taken. But still he should do it by himself.