And then paste this into /etc/grub.d/20_plop:

#!/bin/sh
set -e

. /usr/lib/grub/grub-mkconfig_lib

prepare_boot_cache="$(prepare_grub_to_access_device ${GRUB_DEVICE_BOOT} | sed -e "s/^/\t/")"

PLOPPATH=$( make_system_path_relative_to_its_root "/boot/plpbtrom.bin" )

cat << EOF
menuentry "PLoP Boot Manager" {
    $prepare_boot_cache
    linux16 $PLOPPATH
}
EOF