Not even the considering code this- idea is terrifies me. Allowing ANYONE one to log into your account is dangerous. What if this person logs in and then copies /etc/password & /etc/shadow? You mention that you will change the passwords weekly. Cracking a password can be done in less than a day. You have just given someone an opportunity to brute force root. After I get root, I can spam and get your server blackholed. I can start removing any files I deem unecessary. I can add root kits at will. Being a sysadmin and securing a server is tough enough, why make it any harder on yours?
Moral of the story- don't allow anyone to log in as you.