First off, more
Soul Vault items since it's another layer of protection that they need to bust in order to try this tactic. Adding some constant
Protective Spirit items to reduce surprise backstabbing and
Sandals of Quick Reaction to make it easier to survive the surprise round would also help immensely.
If this keeps getting worse some major head
Shadow Piercings would be a good buff; I think we're still missing a profane bonus to will for most characters.
Kinsight Goggles and group patrols could also mitigate stealth kidnapping. They'd need to get both partners at once to ensure word wouldn't get out.
For at risk PCs a
Guardian Gorget loaded with something nasty would also be a viable approach. It's basically a glyph of warding you keep around your neck and can activate as an immediate action even when an attack would have otherwise rendered you incapable of taking action.
Putting a
Leshy Swarm is probably good enough, though honestly this kind of thing freaks me out enough that I don't have a problem with inventive solutions.
If we could somehow swing a version with greater glyphs of warding we could make some really pointed statements about how welcome this shit is. I bet you that this wouldn't happen again for a while if the next guy to try it ate
Wooden Blight ,
Extract Water Elemental, or
Fleshworm Infestation.
Normal minions can use lesser talismans and
Wax of Defiance until we can find a better solution that stays cost effective.
Some party poppers full of
Cockatrice Grit would also be useful capture tools for grabbing possessed people and exorcised devils/demons/etc. Some
Stone Salve would even remove the need for a caster to be on hand to un petrify them.