The question is: how to handle it mechanically...?
It's not actually tough. You're still dealing stress (perhaps mental to represent an attack at the core of their being). I would probably deal with it in the take out result.
So, you'd take out the human vessel and the spirit joyrider and then rule that the human is unconscious but unharmed, the spirit is dead or shunted to the NN? Simple solution.
What specifically are you referring to Orladdin?
Problem 1: Kravos' ghost wasn't a mook. The fact that 'it took more than one exhange' to exorcise him is thus moot. It would take more than one exchange to burn through his stress and consequence tracks with effective attacks.
Problem 2: Harry's 'Not So Subtle...' aspect makes it incredibly difficult for him to use any but the most blunt applications of Spirit, the element proposed for this effect.
3. Does it fit cleanly into one of your evocation elements?
Fire is supposed to have a purifying aspect (just like water is entropy, and air is movement, etc).It'd be tricky to bathe a target body in fire and not harm the body itself, though.