Yeah, wipe root and stick your new flavour on it - just make sure you don't overwrite the lvm by accident: if you're not used to the way linux names or describes disks, then it might be safer for you to just pull the sata cable prior to the re-install and use the below to mount/automount it.
should be pretty obvious which node in /dev/mapper is the old volume.
# vgchange -ay
# mount /dev/mapper/whatever_your_old_lvm_was_called /your/new/mount_point
To auto mount, do something like
*note*, the double ">>" is very important... don't use a single ">"
echo "/dev/mapper/<whatever> /<mountpoint> <filesystem> defaults 0 0" >> /etc/fstab