Controls in science are relative to something. If you want to verify mindfulness meditation, you have to compare it against something else, something as similar as possible.

I used the phrase 'placebo' informally for the process of controlling against something as similar as possible which lacks the specific content you want to verify. I gave an example of acupressure (which has been done). You gave your own example of how to control against benefits being from meditation rather than the mindfulness modality of meditation.