1. Guidelines of the World Medical Association aren't Swiss law, and I would imagine that Swiss law would take precedence in this case, thus nullifying the physician's right to refuse force feeding the prisoner on hunger strike. The question is, whether the Swiss would bring charges against the physicians for refusing, and actually carry through with prosecution, given public opinion
2. I read a Wikipedia article yesterday regarding Gandhi's use of hunger strikes against the British colonial rule in India. Apparently he was prepared to die for the cause, but the British wouldn't allow that as it would make him a martyr due to the public sentiments in his favor. The article didn't say what the British did, but perhaps he was force fed as well.
3. An additional clarification about US law, as I initially brought up the Constitution and Supreme Court decisions. There is a parallel legal system in the US called the Uniform Code of Military Justice, which applies to serving members as well as prisoners in a military jail. It trumps the US
Constitution as long as one is serving in the US military. I could not find a citation for force feeding and the UCMJ, but that is worth looking into if interested.
4. I looked into the medical aspects of force feeding hunger strikers, and why it is considered torture by organizations like the ACLU, or at least unethical by WMA, the UN, and others.
Most material concerns the thirty hunger strikers at Guantanamo Bay, and a letter written by the ACLU to the US Department of Defense outlines the medical concerns:
http://www.aclu.org/human-rights/aclu-calls-end-inhumane-force-feeding-guantanamo-prisoners
An article in The Lancet notes military ethics and the role of physicians in force feeding:
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(09)62009-2/fulltext
5. While the US has signed the Geneva Convention on Torture, and force feeding prisoners can be considered torture according to the medical community, I am aware from having worked for the UN (in New York), that global Conventions are not enforceable on individual countries, like laws are within countries. The same would apply to Switzerland, which I assume has also signed the Geneva Convention on Torture. It will be interesting to see how this all unfolds.