Oh, I was thinking it had a variety of uses.
The sort of virus installation for later use, a la Knife of Many Hands, being one option, and the easiest to cancel out with a chorae. Think virus scan that removes maleware.
But another option would be to compel the subject to do something right now, a la Xin. This would be unaffected by a chorae post-event, as the lasting mental effects of doing the action would be mundane rather than magical.
In that way, I think Kellhus could easily convince a particularly important individual to put down their chorae, manipulate the piss out of them via CoC and Dunyainic Mageries, then send them on their way.
Its super convoluted, nothing we have seen really suggested that anyone he had that much time with could withstand his will anyway ... But maybe for a lesser man it'd have more use.