If I'm interpreting your allegation correctly, that would be a serious crime. I could conceive of that happening in the early days, but Jim has tens of billions of dollars now. I don't know why he'd risk spending the rest of his life in prison for an extra 1-3b a year.
Also, you've misunderstood the charges on Bluecrest. Platt may also have been doing the scheme you described, but that is not what the SEC fined him for. He would be in prison had he been charged with what you allege.
Except Madoff had to conceal an accounting hole. If he ever stopped, his investors would ask for their $x back, and he would have to give them $0.5x. I know there's a lot of room for cynicism in the financial world, but you still need to know what is happening for each type of fraud or misdeed or good action.
Also, you've misunderstood the charges on Bluecrest. Platt may also have been doing the scheme you described, but that is not what the SEC fined him for. He would be in prison had he been charged with what you allege.