Let's see you access the local admin account without running .exe files while you have a RAT from IT deployed in your system to watch your every click if they choose to do so. I don't pretend to know everything, but from my experience, it doesn't matter if the computer is started without a network connection, if the group policy has been enabled efficiently, it should remain in effect even if the device is disconnected from all networks. So, until you can provide evidence that accessing the local administrator account on a computer with unknown credentials would enable you to override group policy in a timely manner (less than 10 minutes), your whole argument is pointless.
The only way to accomplish the OP's task is temporary workarounds as once a breach is detected, credentials could simply be reset and eventually, the user would be caught if he chose to repeat this task. The OP states that the device is an immobile desktop at his school. The amount of work you are suggesting to put into this task for the end result is unreasonable.