I wrote this after the case of a Washington Post reporter, Hannah Natanson, was compelled to unlock her computer with her fingerprint. This resulted in access to her Desktop Signal on her computer, revealing sources and their conversations.
(I've put a copy of this text at the top of the thread, since it's standard for Show HNs to have some intro/background up there. I hope that's ok with you!)
Hypothesis: If you can assign different fingers to different accounts, you could use (for example) your middle finger to switch to a "panic account" whose automatic login procedure includes disabling Touch ID.
Or, to avoid arousing suspicion, link the most common "login finger" (pointer finger?) to the account that locks down, and use your middle finger for your normal account day in and day out.