Yeep is exactly what i mean, they buy from external sources, and price will be unaffected, then they dump into exchanges coins and prices will drop like stone.
Ofc this will happen behind closed doors and far away from regular people view.
We can see these effects even today after MtGox stolen bitcoins. Who knows how many offshore companies own millions of bitcoins.
I give one simple example. Look at Winklevoss twin brothers, they bought their bitcoins from auctions, so bitcoin price was unaffected when they pumped those money at that time period. And examples can go on forever.
What's the problem for them if the price goes up after buying? If they want to buy a large amount, they can open accounts in several exchanges and see how their investment is revalued instantly. The OTC deals can be interesting for them if they can get a price quite below the market price, if not, I think the exchanges are a better option for them.