This is a bit self delusional. "Use your opponent's strength against
   him", sway pools to support your cause. Or better yet: start pools with
   possibly negative profit. Pay-per-share but you payout a tad more than
   you actually could. That way people will consider your service the most
   profitable, ergo the best, and flock to give you shares at an extremely
   discounted rated (it only costs you whatever you add to it).
   Better yet: force existing pool owners a: out of business, b: to
   support you!
   Better yet: subvert pool managing computers! Make the machines support
   you! Or do MITM attacks to get the shares instead of the pools!
   Maybe just subverting the developers (enough are US based, hint hint)
   to write a teensy exploit.
   Just cracking the central exchanges and everything that accepts Bitcoin
   will also cause a rather big stir. A small division breaking into
   bitcoin-accepting services and selling the bitcoins will lower the
   price directly and decrease trust significantly.
   Visa and Mastercard not providing services to Bitcoin accepting
   customers would also be quite effective.
   Bascially, the cost is lower legally than it is otherwise. And a 51%
   attack can be solved with a trust model, should people wish to do so.
   Lastly you must imagine there's plenty of computing power available to
   most governments on that list. Temporarily using that power for the
   time of the attack is a fairly good idea (depending on what you want to
   do with a 51% attack), and not the full price at all. A cost/hr would
   be much more useful (imho).