YOU CANNOT. Unless, you use the numbers from the "deposits" (which ARE NOT yours to use) When someone deposits, the money goes into the exchange (it should be segregated but in the failures of exchanges it does not seem to have been (even corzine was not doing seg properly). If you were doing this, you are basically "borrowing" others money and using it to short to make the commission to keep the flow going).
That can't be legal.
Really? how naive are you? Mt Gox is following the money laundering laws but name the organization that is regulating how they conduct business? You are complete fools if you leave deposits there. The winklevoss' did not not (and they are spoiled idiots) and yet you do?
Anyone can make a bold claim.