Now that v0.4 of the bitcoin client has encryption I've gone ahead and encrypted the keys in my wallet. But I had previously made backups of my (unencrypted) wallet and those keys are the same keys that are now encrypted.
This gives me a false sense of security.
Is there any way after I've upgraded to v0.4 and encrypted to force all my existing keys to become invalid and then to spend to a new (encrypted) key so that even if an attacker gets ahold of my backup that my coins are safe?