The answer is to store your wallet using TrueCrypt (http://www.truecrypt.org/)

Using the hidden volume facility you can create one 'container' which has two 'partitions' (volumes) each one having it's own password.  In the 'innocent' volume you could put a wallet containing a tiny amount of BTC for plausible deniability and in the hidden volume you put the wallet containing your massive stash.

When you're asked to reveal your password you give the password for the 'innocent' volume containing the wallet with the small balance and you've complied with the regulations/court order/whatever.

No-one can prove whether the TrueCrypt volume contains a hidden volume or not because without the password to decrypt it it's just random noise, which is what a TrueCrypt volume would contain with or without a hidden volume inside it.

Regards
MonkeyThink