shrinking root partition and using free space to create a block device

We are intending to protect a set of user specified files using LVM mirroring where the protected space on which the user files are stored is mirrored on an LV on a different disk. Our problem is that for a user with a custom layout has installed linux with 2 partitons for swap and / and there is no other space available on the primary disk where we can store the files to be protected tht is mirrored across other disk, so we intend to allocate some space on the primary disk that can be used as a LV that is mirrored across an LV on different disk.
What can be done in this situation?
For now we thought of the following:
1> Shrinking the root partition to get some unallocated space that can be used to create a PV.
problems :
a. How do u do it? Can gparted be used online without the live CD?
b. How much can the root be compressed without the OS failure?
2> Can the root partition be converted into a LV?
3> There is free space on the root partition. Now can we use this free space to create a block device that can be converted into PV that would contain my protected files mirrored across other LV on a different disk. If so how can we do it?
Can anyone help me with this?
Thanks a lot.