I would definitely caution him against doing that. He is taking on all of the tax liability if he does their trading in his account. I think the IRS is going to come down hard on people that have not reported this stuff. They used the same techniques to track down foreign bank account that were being used for tax avoidance. At best, he should help his friends set up their accounts and even manage them for them if he wants but the activity occurs under their names so they hold the tax liability.