I'll duck the first point, because I don't know enough about those regulations. Ideally, that would be unnecessary. It should be possible for the rewards mechanism to do all the work.

The way Stacker News referrals function is that you only get a fraction of your referred stackers' rewards. Similarly, Predyx could do something like rewarding a fraction of the referred users' spend (fees + losses).

You don't want to incentivize creating a master account that just receives rewards from active accounts, though, so you may want to also cap the possible earned rewards based on the actual activity: i.e. I need to spend (fees + losses) at least x in order to receive x in referral rewards.