Migrate Ext4 / partition to LVM part. with initrd support on rpi2

I am trying to boot from LVM partition on rpi2, still without success.
I have this steps done :
1/ create base image with dd image to SD card (~4GB)
2/ create LVM partition, volume group, logical volume
3/ dd if=/dev/mmcblxxp2 of=/dev/rootdg/root
4/ changed cmdline.txt for root=/dev/mapper/rootdg-root and fstab changed

And here is a problem … I tried change initrd via some configs but without success {updated with a system update-initrd utility}.
Please, do you have some “cook book” or idea for a build initrd under ubuntu mate or some tips where
(local/pre directory) LVM should be used ? Because Wheezy documented this file : /usr/share/initramfs-tools/scripts/local-top/lvm2.

Thank you.
Filip Matejicek