Can I force my wallet to only have news keys, post-encryption? 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?
Seems to me that the easiest way would be to create a brand new, encrypted wallet using the new client, then send all your coins to that one and forget about the old one.

(You can force a new wallet by simply deleting wallet.dat before launching the client)