That's just the inverse of going long on a stock: Other people observe you buying up many shares of a stock, causing the price to go up, which in turn causes your long bet to come through. The degree that this changes the market depends on how well-respected a trader you are.

For example, if Warren Buffett invests in a company, that company's stock generally rises. That's why Warren Buffett was able to get sweetheart deals when he made short-term loans to Goldman, Sachs and Bank of America recently. They were willing to pay him billions of dollars just for his imprimatur. Buffett received options to buy shares of their stock at the much lower, pre-bump price.

It's not really stock manipulation, though. If you're big enough, or respected enough, you have to expect your trades to move the market.