If i'm reading this right, you don't need to tamper with your HotMail account.
All you should need to do is remove the cookie that it dropped on his system.
Do you know how to do that?
If not, what browser are you using?
Another option is to log in to your HotMail account on his computer.
When you do, be sure the check boxes asking to remember passwords, names, etc, are NOT checked.
Then log back out.