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 this, I think this idea is the most appropriate and wise way for you and your friend.
Give him an understanding of the cryptocurrency market, that way, there will be no problem later.