Have you tried adding a another same disk to existing rpool mirror, then after that using zpool split feature ?
According to the documentation, it should be available on solaris 11.1
https://docs.oracle.com/cd/E26502_01...yrd.html#gjooc
A mirrored ZFS storage pool can be quickly cloned as a backup pool by using the zpool split command. You can use this feature to split a mirrored root pool, but the pool that is split off is not bootable until you perform some additional steps.
If you have other zpools on that LDOM, you will need to do the same with them.
I would advise tho, not to have network active on the new LDOM you are importing the split ed rpool, due to IP and other enviroment specific information is not changed.
After you get it to boot, change the ip address, hostname for your new environment, then add vnets and reboot.
I'm unable to find in documentation these additional steps mentioned tho, but you can try it and see what errors you get (on test ldoms).
If you have unsolvable problems, i will try the method myself to see if any problems exist and get back to you, but i leave the first fun for you