I'd like to make a paper backup of my Armory wallet that will still require a password to recover. Right now it seems that the paper backup is not encrypted.
As the paper backup consists of two simple string you can use any encryption scheme you'd like to implement this.
This can be as simple as manually applying rot13-like encryption, to one-time-pads. Just make sure you keep the ciphertext short in order to still be able to print and, more importantly, type it in eventually.
As Nick mentioned, I'm not a fan of encrypted paper backups. Instead, I added "Fragmented Backups" to the new version (0.90-beta, posted a few days ago on the website), to give the user flexibility in balancing physical security & redundancy without the high risk of permanent coin loss. After all, 95% of the emails we get are users who forgot their password. Many of them didn't even realize that their paper backup protected them against that. As far as I'm concerned, that's the number one reason to make it.
Of course, doing it this way does reduce physical security, but that's far from the biggest threat to most users. If you are concerned about physical security, I recommend you explore the fragmented backup system in the new releases, which addresses these concerns in a robust and "responsible" way.