The home folder encryption uses two passwords: one password, which is the login password that encrypts/decrypts the mount password. The encrypted mount password is stored in the file wrapped-passphrase. This way, if the user changes the password, only the wrappend passphrase needs to be re-encrypted.
I am using Ubuntu 11.10, so depending on your distribution, the commands may be different.
ecryptfs-unwrap-passphrase /home/username/.ecryptfs/wrapped-passphrasesudo ecryptfs-add-passphrase --fnek (use key from above, copy second key, that is displayed)sudo mount -t ecryptfs /home/.ecryptfs/username/.Private /tmp/username