Comment by webstrand

There is, I use kexec to boot a modified cpio containing the fde password, since cpio can be extended by concatenation. https://gist.github.com/webstrand/381307348e24c28d5c4c9a5981...

It's the same technique grub uses to forward the FDE password to the initramfs after its own initial decryption (to read the kernel and initramfs). This works to reboot remote servers with FDE, without needing a vnc or earlyboot-sshd.