I see two problems with this:

First, the boost in mental energy you get from a placebo effect is likely to diminish as time goes on. Your initial enthusiasm will cool and you will get more and more used to whatever ritual is the basis of your placebo effect so it will have less of an effect on your thinking.

Second, the amount of mental energy you need to overcome whatever akrasiatic temptation you are facing varies from day to day and is quite high on some days.

So eventually what is likely to happen is that a day will come when your placebo effect does not work for you. After that, your faith in the placebo will be undermined and it will be even less effective until it completely peters out.

Does this process happen in real life? I think so. I've tried more than one self-help technique which seemed to work for a while and then stopped working after a while. I think most people who have tried to improve themselves have had similar experiences. In fact, I would guess that PJ Eby's own self-improvement campaign hasn't been going all that well.

So to succeed, one needs to understand and address exactly (or nearly exactly) what is going on in the mind. As Eliezer would say, you need to come up with a generalization that explains both the rule and the exception.