When you get banned from life from Adwords, it’s not your computer or IP that is banned. It is you personally. Google is very good at making connections, so if you ever use an account, a computer, an IP, an address, a credit card an email or any other device or information that was ever, even remotely associated, you will be banned again. This includes computers and accounts owned by friends and associates.
I had one client that got his account banned because his brother, who was previously banned from AdWords, used his computer one day to log in and check his email. Now he can never open another AdWords account associated with himself because he is associated with his brother who earned the original ban.
Sadly, using your friend’s AdWords account probably added your friend to the “banned for life” club. Just being associated with a banned person will get you banned.