A lot of incorrect information:
a) Giving 7.5k to someone else is not money laundering. Bollocks!!! What they do with the money they received as gift is up to them. If anything the recipient of the gift may have to declare taxes on those. But guaranteed it is not money laundering. By the way, let me school you on some facts: No broker in the world will ask you where the money is from that you intend to fund your account with. Why? Because it is not required by law and hence is irrelevant. What is very relevant, however, is that your bank asks you where the money is from when you receive certain sums in your bank account. Why? Because they are required by law to do so. So, you receiving money from someone is not money laundering. Nor is it if you deposit the received money in your bank account. And it is also not money laundering when you turn around and transfer the deposited money from your bank account to your brokerage account.
b) You just said John opened an account in his name. So he is the beneficial owner of the account. He can do with any of the proceeds as pleases him. If he returns money to you as a gift then you may have to declare certain taxes. But again its not money laundering.
c) By the way you can open both accounts with different brokers in your own name. Nothing speaks against that and because you are not acting illegally by shorting in one account and longing in another account you do not commit any fraud or criminal act whatsoever, no John involved.
d) Here is where you are being stupid: Even if you opened two accounts in your name with different brokers, with the EUR/USD example you are long 17.5k and flat in the account (given as OP laid it out, that you are forgiven negative account balances). So, you are in no way flat but up 2.5k. This whole story has NOTHING whatsoever to do with whether you involve another individual or do it all on your own. You are missing the point completely.
Your claim of charges is utter bullshit. Sorry mate, but you already messed up the whole story, there is no wire fraud nor money laundering going on at all. Again, you do not need to involve any John, and even if you involved another individual...in Germany, for example, you can give 1 billion Euros to whoever pleases you as long as applicable taxes are paid (inheritance or gift giving, or what have you). I am almost sure the same applies in the US, Japan, France, or any other country as well. Your law degree utterly fails you here...