PA,
Why is the PVR option more messy? I don't know if it will change under NEM, but it used to be that once you were over 50 you could PVR with 6 months notice to leave. Given the amount of resettlement you would be entitled to, and terminal leave, it comes pretty close to PVRing and then clearing your desk straight away! That doesn't seem at all messy to me.
I can't see any desk officer being able to make any guarantee to anyone prior to them making their decision, if for no other reason than at that stage the desk officer won't yet know how many will ultimately stay or go, and won't know how many cards he has to shuffle the deck and fill his slots.
Edited to add:
Ah - I've just seen JTO's post, maybe that's why the PVR option becomes messy?