Can I buy/sell a lot of bitcoins without moving the price?
It won't work, no matter how you do it. If you acquire a lot of Bitcoins, that will mean that a lot of people who wanted to get rid of their Bitcoins no longer want to get rid of their Bitcoins. Thus, they will stop supplying them. The reduction in supply will move the bid/ask prices. It's fundamental economics and you can't change it.