install to an lvm partition

Hi all
installation problem
I am trying to install 17.12.2 KDE to an existing/new lvm partition on my existing main volume group.
I cannot replace the existing volume group as it contains active operating systems
Any ideas on how I could use the installer/CLI to achieve this?

have tried
~# cl-install -D /dev/mapper/“path to drive”
~# cl-install -D /dev/“volume group”/“path to drive”
both return error in parameter -D “then a list my physical drives as accepted parameters”

hope this helps