In reply to thomaspomfrett:
Just a quick note to make things a bit easier. If you do end up abbing with the v sling (can't remember the proper name); Stay and clip them in from above them. In most cases it's easier to pull a person up towards your y sling than to push them up to it.
Getting the length of the slings right is important too. You'r supposed to have the shorter side available to clip to the casualty, so theoretically they will be sitting on your lap once the are released. If you do that correctly then you almost sit side by side maybe get a knee underneath them and push them up to the clip. Both these methods should make the safety line slack enough to remove it.
On another note, with the stirrup hoist mentioned above is needed (if all else fails, but unlikely). Rather than using a prussik you can simply clip into your belay carabiner another carabiner. this way also pulls the casulty up and towards you.
Just thought, if you think you need to do the stirrup lift, it is easier to stay above them and clip the v sling into them thus taking the weight off of the safety than it is unclipping the safety and then them potentially dropping onto your line if you don't lower the stirrup slowly.
Also think about what rope you're using to ab down on. Dynamic, static. Stretch will make a difference on bigger abs if you're trying to get them from their dynamic safety to your (theoretical) dynamic ab rope.
Sorry for writing such an easy! Just my minds musings on the subject!