In instances both you and the customer require root access you can build them a secondary root password this will have to be done from the current root login;
First add the user
adduser root2
Give the new user a password
passwd root2
Change the permissions of your new login
vi /etc/passwd
Scroll down to the bottom where your new login is created and change it to the following;
root2:x:0:0:root:/export/home/root2:/bin/bash
Quit vi (esc followed by :wq! should save it)
Now test and confirm it works.