You could always set up one pin/passcode for two factor auth and then use a separate passphrase as a fallback to unlock the device. It woould be much better security that way.

Also while we are on the subject using a short pincode to unlock the device is asking for trouble. While the device ID is tied to the decryption and there is no way to extract it yet I have no confidence that it will remain that way forever. At which point the ability to crack a short pin off the device means the pin will get cracked in seconds.