Mrdeano is right in his comment. the technique may have worked better if you stated that a particular type of juice is great for inducing lucid dreams if you have it before bedtime. Then you could have made some elaborate scientific lie about why it works. Self-deception is a bizillion times harder than being deceived by others, and the technique that you are proposing is that someone ought to deceive themselves into believing something that they know is a placebo, actually isn't a placebo and is really somehow effective via means of placebo.
If someone succeeds with the technique then there is a good chance that their belief in the 'lucid potion' is reinforced. But if you fail, it takes even more self-deception to make the technique work.