That's the idea. You don't. Either you generate the key some other way and write it into the device (but it cannot be read again), and backup the original; or

That's the idea. You don't. Either you generate the key some other way and write it into the device (but it cannot be read again), and backup the original; or you generate it on the device and do NOT back it up - instead you make a back-up key, and authorize both keys rather than just one. I don't know if this supports external key. YubiKey does.