I don't believe it's possible to do that. Something needs to make the volume group and root lv available which is normally done by vgscan --mknodes and vgchange -ay in the lvm enabled initrd. Besides, something would have to tell the kernel which lv is the rootfs.

The way I do recovery with a root on lvm system is as follows

Boot from Install CD, enter whatever options you needed when you did your initial install (if any)
Login to the install environment as root and then from the command line.

vgscan --mknodes
vgchange -ay
mount /dev/rootvg/lvroot /mnt
mount /dev/rootvg/lvusr /mnt/usr (and so on for any other filesystems you have)

... then either fix things manually under /mnt or if you need to run from your normal system environment directly

mount -o bind /proc /mnt/proc
mount -o bind /sys /mnt/sys
chroot /mnt


If you want to avoid all this messing about, then your best bet is to keep a second 'recovery' setup in your lilo.conf using a known good kernel and initrd which you should never change after you get it running.

Thanks a lot, that made things clear