Prerequisite: Tails with an amd64 kernel (e.g. from current experimental branch).

Tested with grub-efi 2.00-22 from Debian unstable.

sudo apt-get install grub-efi-amd64-bin

# make the system partition an *EFI System Partition* (ESP)
parted "$TAILS_DEVICE" set 1 boot on

    MODULES="
       all_video
       bitmap
       bitmap_scale
       boot
       btrfs
       bufio
       cat
       chain
       configfile
       crypto
       echo
       efifwsetup
       efi_gop
       efinet
       efi_uga
       ext2
       extcmd
       fat
       font
       gettext
       gfxmenu
       gfxterm
       gzio
       halt
       hfsplus
       iso9660
       jpeg
       keystatus
       linux
       linuxefi
       loadenv
       memdisk
       minicmd
       normal
       part_apple
       part_gpt
       part_msdos
       password_pbkdf2
       png
       read
       reboot
       search
       search_fs_file
       search_fs_uuid
       search_label
       sleep
       terminal
       test
       trig
       video
       video_fb
    "

mkdir -p "$TAILS_MOUNTPOINT"/{boot/grub,EFI/BOOT} && \
   grub-mkimage --output="$TAILS_MOUNTPOINT"/EFI/BOOT/bootx64.efi \
      --format x86_64-efi $MODULES

cat > "$TAILS_MOUNTPOINT"/boot/grub/grub.cfg <<EOF
menuentry Tails --class start {
    echo $"Loading Tails..."
    linux /live/vmlinuz2 initrd=/live/initrd2.img boot=live config live-media=removable nopersistent noprompt timezone=Etc/UTC block.events_dfl_poll_msecs=1000 splash nox11autologin module=Tails quiet
    initrd /live/initrd2.img
}
EOF

• boots on ThinkPenguin Royal
• boots on Macbook 13-inch Mid-2012 with rEFInd; one has to choose Fallback boot loader from Tails in rEFInd, Boot Linux from Tails does nothing at all