The reality is that we don't have advanced enough financial products nor a sophisticated enough market to allow bulk transactions to occur without a price impact. The market is too thin and dark pools are impossible because every single transaction is both broadcast and verified.
If a large amount of Bitcoins are suddenly transferred from a single account, then everyone knows in ten minutes. Accounts would have to be highly divested and decentralized to hide a bulk transaction. Thus, the analogue to Iceberging. I can imagine a specialized set of market actors offering this service for large cap investors, but honestly we need options to trade risk way before we worry about large transactions.
My advice to anyone who holds several thousand Bitcoins who got in early is to wisely divest until they have recouped their initial investment and then adopt price points to slowly liquidate their holdings. It's a deflationary currency. The price has to go up if it is going to survive. Don't worry about daily fluctuations.