I think my definition of NDT above was worded badly. The problematic part is "if he had previously known he'd be in his currently situation." Consider this definition:

You should always make the decision that a CDT-agent would have wished he had precommitted to, if he previously considered the possibility of his current situation and had the opportunity to costlessly precommit to a decision.

The key is that the NDT agent isn't behaving as if he knew for sure that he'd end up blackmailed when he made his precommitment (since his precommitment affects the probability of his being blackmailed), but rather he's acting "as if" he precommitted to some behavior based on reasonable estimates of the likelihood of his being kidnapped in various cases.