I used to have a custom NAS with full disk encryption, whose bootloader would spin up a tiny SSH server with very few features, mainly only access to an unlock function that would allow to transmit the encryption passphrase over the said SSH tunnel. Then the SSH connection would be closed by the server and it would startup with the decryption key.

That way, it was impossible to access the data physically, but I was still able to reboot the box whenever I wanted without any problem.