Also your forgetting a very important factor when it comes to danzo perfoming his curse seal.
It was noted by Obito when sasuke fought danzo, a panel was shown where danzo first had to make close physical contact with sasuke first by grabbing his throat and that was when the curse seal was put on sasuke.
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^^^ Proof right there. If danzo plans on putting that curse seal on Kakuzu he will first have to make physical contact with him by touching him, similar to sasuke I assume via throat? Either way it wont be a easy task.
EDIT- ima go hit the hay im tired as fk so dont expect a reply.