If you take out your weapon (sword and shield) get really close to the cell door, hold the left trigger and then stand so that the shield is through the door (by the way you need at least sword skill level 7).
Press A+B simultaneously and then right trigger, you can go through the door.
It may take a few tries, but I have done it many times on different doors, even stone ones.
Xbox360Cheats.com is an unofficial resource with Xbox 360 cheats provided by members of the public. We are usually unable to test submitted Xbox 360 cheats, so please use them at your own risk.