system installation - reinstall ubuntu without rebooting on usb pen drive

I want to know if it is possible to reinstall ubuntu server edition without rebooting on an usb pen drive. I have LVM and I want to install the new version on a new LV, then change grub2, and then reboot.

Actual config:

1. LV root1410: Ubuntu 14.10.2 (current working system)


2. LV root1504: Ubuntu 15.04 (target system)

Ok I have to add a menu entry for grub2 in /etc/grub.d/40_custom and then run update-grub. I know how to do it for a simple partition, but not how to do it with a mdadm & lvm combination.

menuentry "Ubuntu 15.04 ISO" {
 set isofile="/home/serge/Downloads/ubuntu-15.04-desktop-amd64.iso"
 loopback loop (hd0,7)$isofile
 linux (loop)/casper/vmlinuz.efi boot=casper iso-scan/filename=$isofile noprompt noeject
 initrd (loop)/casper/initrd.lz
}