Is there a way to wipe a device based on a certain password? A like a "Wipe-me" password? Is there a way (an app perhaps) that will wipe a phone if a certain password is entered at the lock screen? For example "letmein" unlocks the phone, but if you enter "wipeme" it will start the factory reset process, or erase the decryption key or what have you.
There is no way to do this, although you could do it using SMS.

You would have to install an app like Cerberus which allows you to send an SMS to wipe your device.