written tutorial
Here is exactly what I do to make it work
1. Completely become another character. This includes skin, fighting style, faction, AI.
2. Have a save file in the school
3. Load that file.
4. Get down to extremely low health near 3PM and stand on the second floor, near a ledge where you can drop to the first floor.
5. As soon as the clock hits 3 jump off and you will get knocked out.
6. Wait. Don't do anything, don't press anything, don't move the camera around etc.
7. You should become another character at around 4:00-4:15. If it doesn't work then repeat.