In our company, "falsification of documentation" is one of

the fastest ways to get fired. (Others are doing drugs or bringing fire arms to company premises.) Whatever you do, do NOT ask someone who is NOT you supervisor to pretend to be your supervisor. If you can find a colleague/friend/teacher who is willing to write the letter for you, politely ask them to write it as your colleage/friend/teacher. Credit is easy to lose and very hard to earn back.