Ms. Sparrowmoon,
I was flipping through Strange Occurrences (A Practical Guide to Dealing With the Unexpected, Unnatural, and Just Plain Weird in Everyday Life) the other night, and I had a question. You mentioned that it's possible to separate a ghost from its focus by placing a persistent blessing on the object or place to cause a... well, comparable to an allergic reaction in the ghost.
I think you're absolutely right about that, and have tried it with some success. Here's another option that I've found has been fairly reliable. Due to a peculiar quality of my aura, it's pushed almost entirely off the astral plane and onto the shadow plane. This is mainly due to a combination of a sort of astral birth defect and an occupation that's causing a few changes.
What's really interesting is that I applied the principle you mentioned above to another situation. I started keeping a few weak healing potions around, and told my familiar to administer one at the next opportunity. Ordinarily he helps push them away by force, but the next time I had a problem, I managed to weaken the group of ghosts' hold by drinking the potion. Made my aura just toxic enough that they weren't interested and I was able to get things stabilized again.
My question has to do with the effectiveness of this technique on normal people. I've not had an opportunity to experiment on a live subject, so all I have is a hypothesis. I'm guessing that it would be more effective on a live subject, since their aura is better equipped to absorb the positive energy than mine is.
However, the reason I'm not certain is that a normal person's aura is already a little closer to the positive energy plane in the first place. Perhaps without the jarring introduction of a radically-opposed energy type, the ghosts in possession of the body wouldn't be weakened as significantly.
Do you have any data on this? I think I've gone as far as I can without test subjects of my own, and so far I haven't found any humanoids wandering around possessed by whole gangs of incorporeal undead that I can take home and experiment on. Maybe you've had better luck or some other ideas. Either way, I'd love to hear back from you.
Thanks for your time,
Zea H. Mazuo