Realistically, if you had that much BTC to sell it would be wisest to do it in phases, or better yet, tiers. Offer volumes of BTC at various "outrageous" price levels (eg, $5 over market, $10 over market) and make sure you put a substantial amount of volume at each price level. Whenever the market surges you'll cap the exchange rates at your price levels until all your volume is depleted. In fact, you can see people already doing this on some exchanges...
A guy used MtGox to sell 5,000 BTC the other day, and caused a small dip - about 15%, if I recall. That's about 500k USD out in an afternoon.
Some exchanges also have "dark pools", designed to allow big investor to get into and out of the market "quietly".