I've just discovered memdisk. It's part of the
syslinux package on Debian/Ubuntu, and hides in
Memdisk lets you boot a floppy image, via grub or pxelinux. In this modern era of computers without floppy drives, it means you can do BIOS updates without having to go through the whole procedure of turning a floppy image into a bootable CD.
In PXELINUX, the config file would look like this:
DEFAULT memdisk initrd=FILENAME.img
In Grub, like this:
title Bios Flash kernel /boot/memdisk initrd /boot/FILENAME.img
Thanks ThinkWiki for the idea.
Caveat emptor: apparently some flash tools don't like memdisk, so YMMV