What evidence? All the evidence I have seen has either been of poor quality, or simply shows the placebo effect is a distraction (eg transient psychological relief).
If you are looking for evidence to link Placebo Effect and its use to the treatment of ME/CFS then it would certainly provide poor results. On the other hand, if you were to look at Placebo in a broad sense, there is support for it being at least in part physiological.
Neurobiological Mechanisms of Placebo Responses
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3073412/
Neurobiological Mechanisms of the Placebo Effect
http://www.jneurosci.org/content/25/45/10390
It is a significant leap to say that the Placebo Effect is purely psychological. It is also a massive leap to say that one can use the Placebo Effect to treat diseases. And an even farther leap to say that one can use it to treat something as complex as ME/CFS. It does not work that way as most with ME/CFS already know.
That being said, it does not discount that there is very real physiology going on in Placebo. Seriously considering this concept though will only make sense if someone is willing to look at Neurophysiology as being dominantly NOT CONSCIOUS with only a small fraction of it being Conscious.
As a result, you may be able to influence some of your Neurophysiology including pain responses, fatigue or nausea but you cannot fix an entrenched physiological disease or pathophysiological disorder with Conscious Thought or Placebo.
I am of the opinion that Placebo is at least in part a real physiological phenomenon. When I say that I mean it in a broad term across all of medicine. I am not speaking specifically to the "use of Placebo" to treat ME/CFS which at best would be a very poor application of it. In another words, it is not going to work.