How about bringing up specific bits of rationality when you talk with them? If they talk about plans, ask them how much they know about how long that sort of project is likely to take. If they seem to be floundering with keeping track of what they're thinking, encourage them to write the bits and pieces down.

If any of this sort of thing seems to register, start talking about biases and/or further sources of information.

This is a hypothetical procedure-- thanks for mentioning that The Simple Truth isn't working well as an introduction.