In reply to JHammond:
I've used a powerbar pullup bar (eg
http://power-bar.co.uk/ ) which works on the same principle for hanging by the looks of it.
It seemed to cause no issues to the top architrave, however a friend who used his more extensively found it did wear grooves in the vertical architrave where the weight pushes inwards. You could probably avoid this with some extra padding, but it might change the angle of the fingerboard.
The main issue I found was the bits that hooked behind pushed in and damaged the plaster on the other side of the door, but this shouldn't be an issue here as they've used a flat bar of wood instead of two pressure points.
Hope that's of some help, if not specific first-hand experience.