"In Chadwick v. Janecka (3d Cir. 2002), a U.S. court of appeals held that H. Beatty Chadwick could be held indefinitely under federal law, for his failure to produce US$ 2.5 million as state court ordered in a civil trial. Chadwick had been imprisoned for nine years at that time and continued to be held in prison until 2009, when a state court set him free after 14 years, making his imprisonment the longest on a contempt charge to date."

http://en.wikipedia.org/wiki/Contempt_of_court#United_States

Claim the exchange operator hired you to rob their own business and they have the private key :P

IANAL, but in the US, the 5th amendment still protects combination locks, and as far as I can tell, passwords.

Prosecutors can be as intimidating as they wish, the government is free to use their magical NSA powers to recover the bitcoin. They can't compel someone to incriminate themselves. giving the wallet address to the prosecutor is effectively admitting to a crime, perhaps just conspiracy, but nonetheless that's self incrimination.

Go for memorization over tattooing.

Plausible deniability. You are only the low ranking front. You don't know the passphrase needed to hand over.