I used that very method to rescue a machine after the contents of /boot were damaged. Booting from a live CD and building a UML kernel (on another drive, there

I used that very method to rescue a machine after the contents of /boot were damaged. Booting from a live CD and building a UML kernel (on another drive, there wasn't enough RAM to do it there & I didn't want to mount any of the main partitions just-in-case) allowed me to boot from the main root and rebuild initrd & friends easily. I felt proper clever!