My nephew used to Captain J41s (not in the UK) and they usually parked on the apron in such a way as to be able to go forward.
If I recall correctly, if a powerback was required the formula was:
- Open the throttles a touch
- When you have travelled 2/3 of the way - close the throttles
- Let her drift to a stop then apply brakes and set the pitch
- DO NOT touch the brakes when she is rolling as she will almost certainly sit on 'her backside' without warning and VERY quickly!