OS X 10.7 Lion: Reset master password to FileVault 2
It's surprisingly simple.


Delete /Library/Keychains/FileVaultMaster.keychain
Delete /Library/Keychains/FileVaultMaster.cer


When you return to set a new password your old one will have been cleared.

Based on step 4 in How to create and deploy a recovery key for FileVault 2.