From what I remember - and that's not much - the Vauxhall Viva HB steering lock only engaged when the key was removed from the ignition. Wasn't this true of most if not all cars at the time? I just turned the key so the ignition was off and left it in place.
To all intents and purposes the engine was running. It was going round and round, but just not using power from exploding fuel to do it. Gravity and the rolling rear wheels provided the power. Braking at the end of the downhill run was no problem, or I might not have been here to make this post!