You are assuming CFD brokers are market makers only. Each broker have their risk mitigation model. I suspect the larger the stock the better leveraged you will get and usually the CFD will know if their client are a big player such as your example and will not bet fully against you. They may hedge a majority of your position through real share participating depending on their risk model and just make the brokerage on your position.
I don't think you are the first to think of such scenario. In addition, this is a risky way to play the market because any gap down each day and you effectively exposed to an uncontrollable hair cut. Guaranteed stop loss cost money each time it is altered.
