[korfuri]

Just give the attorney a sealed printed list of 10,000 numbered passwords. Someone with the passwords won't know what they are for. Even if they can guess that one of them is for your email account and they know your email account, they'll have to try thousands of passwords before they find the right one.

In your house, and maybe with trusted friends, keep the instructions sheet with logins and a reference to the relevant password number. "To access my email account, username is [e-mail] and use password #5122 from the password list".

[ericpauley]

You could also use a simple one-time-pad here to split the password. Generate two alphabetic passwords, one for your attorney and one for a trusted friend. Actual password is these mixed with alphabetic rotation character-by-character (anyone ought to be able to figure out how to do this given a short guide).

Simple, and provably useless to an adversary unless they have both passwords (aside from knowing password length/format with one).