Also, your way to stop the swings by injecting money into Bitcoin is unrealistic, but I think you knew that 'solution' is not going to happen.
Yes it's unrealistic, but it works.
How do you "play" USD or Euros? You don't. Due to the gigantic market volume it's impossible.
The only profits to be had are either high frequency trading forex bots, or long term holding.
On Mt. Gox, BTC can fluctuate anywhere between 5 to 500% in 1 day just because someone with $200k dollars is placing buy and sell orders.
That's not a stable market.
What would stabilize the market is billions of $ of daily volume.
No single person could fill 50% of all buy/sell orders in the orderbook in a few seconds & crash the price to 0.01 as happened a month ago.