That's a good point. Let me try a different one.
Let X be 'I am slightly more committed to this group’s welfare, particularly to that of its weakest members, than most of its members are. If you suffer a serious loss of status/well-being I will still help you in order to display affiliation to this group even though you will no longer be in a position to help me. I am substantially more kind and helpful to the people I like and substantially more vindictive and aggressive towards those I dislike. I am generally stable in who I like. I am much more capable and popular than most members of this group, demand appropriate consideration, and grant appropriate consideration to those more capable than myself. I adhere to simple taboos so that my reputation and health are secure and so that I am unlikely to contaminate the reputations or health of my friends. I currently like you and dislike your enemies but I am somewhat inclined towards ambivalence on regarding whether I like you right now so the pay-off would be very great for you if you were to expend resources pleasing me and get me into the stable 'liking you' region of my possible attitudinal space. Once there, I am likely to make a strong commitment to a friendly attitude towards you rather than wasting cognitive resources checking a predictable parameter among my set of derivative preferences.'
Then, instead of saying my previous suggestion, say something like, 'I would precommit to acting in such a way that X if and only if you would precommit to acting in such a way that you could truthfully say, "X if and only if you would precommit to acting in such a way that you could truthfully say X."'
(Edit: Note, if you haven't already, that the above is just a special case of the decision theory, "I would adhere to rule system R if and only if (You would adhere to R if and only if I would adhere to R)." )
Wouldn't the mere ability to recognize such a symmetric decision theory be strong evidence of X being true?
If I understood you correctly, I think that people do do this kind of thing, except it's all nonverbal and implicit. E.g. Using hard to fake tests for the other person's decision theory is a way to make the other person honestly reveal what's going on inside them. Another component is use of strong emotions, which are sort of like a precommitment mechanism for people, because once activated, they are stable.
Followup to: Do you have High-Functioning Asperger's Syndrome?
LW reader Madbadger uses the metaphor of a GPU and a CPU in a desktop system to think about people with Asperger's Syndrome: general intelligence is like a CPU, being universal but only mediocre at any particular task, whereas the "social coprocessor" brainware in a Neurotypical brain is like a GPU: highly specialized but great at what it does. Neurotypical people are like computers with measly Pentium IV processors, but expensive Radeon HD 4890 GPUs. A High-functioning AS person is an Intel Core i7 Extreme Edition - with on-board graphics!
This analogy also covers the spectrum view of social/empathic abilities, you can think about having a weaker social coprocessor than average if you have some of the tendencies of AS but not others. You can even think of your score on the AQ Test as being like the Tom's Hardware Rating of your Coprocessor. (Lower numbers are better!).
If you lack that powerful social coprocessor, what can you do? Well, you'll have to run your social interactions "in software", i.e. explicitly reason through the complex human social game that most people play without ever really understanding. There are several tricks that a High-functioning AS person can use in this situation: